Over the last 15 years, infrared (IR) spectroscopy has developed into a novel and powerful biomedical tool that has multiple applications in the field of haematology. By revealing subtle alterations in both the conformation and concentration of key macromolecules, such as DNA, protein and lipids, IR spectroscopy has been employed to investigate multiple aspects of leucocyte physiology. IR spectroscopy has been used, for example, to diagnose and prognose leukaemia; to characterise differentiation and apoptotic processes; to predict drug sensitivity and resistance in leukaemic patients undergoing chemotherapy; to monitor the response of leucocytes to chemotherapy and to perform human leucocyte antigen matching for bone marrow transplant patients. Such studies have provided insight into pathogenic mechanisms underlying specific leucocyte disorders, especially leukaemia. While it is likely to be some considerable time before IR spectroscopy is sufficiently developed to displace the established technologies, IR spectroscopy has the potential to become a valuable analytic tool in basic and clinical haematology.