In a laboratory in St Louis, William Masters and Virginia Johnson rigged up test subjects to electrocardiogram and respiratory monitors and asked them to masturbate. The apparatus was a sort of orgasmic polygraph that meticulously documented, as Thomas Maier puts it, "each pulse, breath, thrust and quiver". The scientists also observed physiological changes in women through a motorised Plexiglas phallus, nicknamed Ulysses, inside which a camera was secreted. It was radical, controversial research for the mid-50s, undertaken with utmost discretion, though there never seemed to be a lack of willing subjects.  Masters and Johnson went on to watch volunteers having sex through a one-way mirror. Wired up like lab monkeys, the couples seldom knew each other; their faces were veiled in paper bags or pillowcases, with holes cut out for the eyes – until Masters's mother made more comfortable silk masks out of the same material as her son's bow ties. Johnson, wearing a white doctor's coat, would occasionally make a discreet entrance to take measurements of erogenous zones. While Masters was aloof and imperious, she was the encouraging, friendly hostess of the clinic. "She made people feel they were doing God's work," remembered one participant.  When the fruits of this research, the bestselling Human Sexual Response, appeared in 1966, Masters and Johnson became instant celebrities. According to one commentator, they were "at least as unshakably fixed in people's minds as Procter & Gamble or Benson & Hedges". The 60s was "the decade of orgasmic preoccupation", as Masters put it, and their book captured the mood of this sexual revolution. Nevertheless, the minutely observed descriptions of sexual mechanics were purposefully couched in Latinate, medical language: "This maculopapular type of erythematous rash first appeared over the epigastrium … " According to Masters, who admitted to having been deliberately "pedantic and obtuse", it was "the most purchased, least read book in history".  Maier's gripping biography, first published in 2009, is essentially a biological romance. In 1971, the research duo got married and were held up as paragons of the virtue of a healthy marital sex life. Despite their celebrity, Johnson described the couple as "absolutely the two most secretive people on the face of the Earth". Maier, who interviewed both at length, keeps us within the cloistered, claustrophobic world of their sex research institute, and the book consequently has a concentrated energy. Only the briefest of sketches are made of the political changes taking place in the country outside. Masters of Sex has been reissued to coincide with the excellent TV adaptation of the same name, a medical Mad Men in which Johnson is played by Lizzy Caplan and Masters by Michael Sheen. His Don Draperish secrets are paternal abuse and a low sperm count.  In 1954, Masters, a bald, greying 38-year-old obstetrician and fertility expert (who had set up one of the nation's first sperm banks), became absorbed in sex research. Appalled by Americans' lack of sexual knowledge, he dreamed of supplementing Alfred Kinsey's sociological statistics with physiological data. Kinsey had published the second of his famous reports a year earlier but, as only an associate professor, Masters still wasn't allowed to view a "pornographic" textbook about reproduction in the Washington University Library. Following Kinsey's lead, he began interviewing, examining and observing prostitutes in St Louis, Chicago and elsewhere. He probably looked through many of the same peepholes Kinsey had spied through a decade and a half before. He soon realised, however, that he needed data from a less skewed and contentious demographic, and he convinced the university to let him set up a secret sexology laboratory.  Two years later, Masters employed Johnson as a secretary, though she was soon elevated to the role of research associate. A former singer, she had been married three times and was a single mother of two children. She had only completed four years of college, and was not an MD, which was the cause of some criticism among colleagues, and of insecurity on her part. But she was able to put volunteers at ease with her non-judgmental, honeydew sincerity; skills the aloof Masters lacked. And she was committed to the work – to which she and Masters devoted evenings, weekends and holidays. Kinsey had crisscrossed America to interview 18,000 people for his reports; together, in their laboratory, Masters and Johnson observed a staggering 14,000 orgasms.  Drawing on observations of 382 women (and 312 men), they refuted Freud's theory of the vaginal orgasm, which the psychoanalyst supposed was more mature than the clitoral variety. Kinsey had already questioned this on the basis of his data, but Masters and Johnson definitively proved that the physiological response in the two was identical. They also pointed out the similarities between the cycle of men and women's responses during coitus, portrayed as a carefully choreographed harmony of increased blood flow, engorgement and muscular tension. Nevertheless, two-thirds of the book concerned the mysteries of women's bodies: the ability to have multiple orgasms (enjoyed by one in six women, according to Kinsey) gave females a certain sexual superiority. Though critics accused Masters and Johnson of hedonism, of unhitching sex and love, the orgasm was now seen as a fundamental right.  Titillated by the voyeurism, they slowly became absorbed in their own research. At Masters's suggestion, they began having sex themselves in the laboratory to test the best positions and techniques. Johnson was 35; her boss a decade older. Later, when asked if it might have constituted sexual harassment, Johnson replied: "It might have been, but I really hadn't thought of it that way back then … He was a senior medical person." Their affair spread outside of the lab and was soon an open secret on campus. When Johnson got involved with someone else, it prompted Masters to leave his two children and wife of 29 years, and marry her. Maier asks whether it was a union based on love or convenience. To lose her would have jeopardised the research.  Initially, the university had allowed Masters to fund his study by diverting fees earned in his fertility treatment work. When they ended this special privilege, Masters and Johnson left to set up the independent Reproductive Biology Research Foundation, later renamed the Masters and Johnson Institute. There they could raise money from fees charged to patients treated for sexual difficulties. (They also received a $300,000 grant from Hugh Hefner, an admirer whose daughter would later join the board of the institute.) Masters and Johnson claimed – on unclear evidence – that half of married couples suffered sexual "dysfunction". To address this they pioneered a treatment that fused Kinsey and Freud, mixing questionnaires with sessions devoted to "sensate focus" – a series of touching exercises – to cure impotence, premature ejaculation and inorgasmia.  Masters and Johnson appeared on the cover of Time in 1970, pegged to a second book, Human Sexual Inadequacy, 300,000 copies of which were sold in the first two months. They charged $2,500 for a two-week sex therapy course, a sum Masters pointed out was cheaper than a few years of psychoanalysis. (They charged even more for use of sexual surrogates, a service only available to unmarried men, though this was stopped when the angry husband of one surrogate sued the institute.) They claimed an 80% success rate and soon had a waiting list of many months, with numerous celebrity and politician clients. But it was never clearly articulated how success was determined, or by whom, and there was a marked self-selecting bias to their optimistic data.  Despite being held up by liberationists as agents of sexual freedom, Masters and Johnson proved something of a disappointment to radicals. They tried to divorce sex from politics and were uninterested in how society shaped desire and vice versa. They were politically conservative and staunch defenders of the "marital unit", as they called it. Masters voted for Nixon in 1968, and was a church-going Episcopalian and registered Republican. Johnson was repeatedly asked to attend feminist rallies, but always refused. "I would never march with the ladies," she said. She feared emancipated women made men feel inadequate, the cause of much of the sexual dysfunction she saw.  Later books claimed to be able to cure homosexuality in 70% of cases (60% of those who sought "conversion" were married), which alienated the gay liberation movement and spawned a myriad destructive treatment programmes, many sponsored by the church. To this end, in the mid-80s they began using surrogates again, even going so far as to persuade one to live with a paedophile for three months in the hope of correcting him. Another misjudged volume, Crisis: Heterosexual Behaviour in the Age of Aids, fuelled the hysteria surrounding the disease, which they claimed was more rampant than estimated, on the verge of an epidemic of biblical proportion, and could be spread by kissing, toilet seats and mosquitoes.  In 1991, the 76-year-old Masters, by then suffering from Parkinson's, suddenly walked out on their 20-year union to marry his first love, a girl he had met on summer camp while a young medical student. Johnson was devastated but managed to put on a brave show of professional unity. However, by then the institute was already foundering. The waiting lists had dwindled and they struggled to pay staff. Looking for a successor, they employed theologians rather than physicians, one of whom was a Baptist minister married to Johnson's daughter, as if they now considered the sexual question a religious one.  The many marriage counsellors Masters and Johnson had trained at the institute left to set up a plethora of competing, cheaper clinics. Strapped for cash, Masters, who died in 2001, considered a premium-rate sex helpline. Johnson, who died earlier this year, contemplated a series of advice tapes with titles such as "Couples and the Power of Intimacy" and "Intimacy for a Lifetime (It's Not Over 'Til It's Over)", but they failed to get off the ground. By then, sex had become a saleable product and the media was saturated with lessons on how to achieve better orgasms. Masters and Johnson had helped to create this new environment of apparent libidinous confidence, with which their own archaic sexual coaching methods now seemed hopelessly out of tune.  • Christopher Turner's Adventures in the Orgasmatron: The Invention of Sex is out in paperback from Fourth Estate.
The TV adaptation is a hit, but who were the real Masters and Johnson? This biography uncovers the story of the couple whose unusual scientific researches – they studied 14,000 orgasms – kickstarted a sexual revolution. By Christopher Turner