In 1994-1996, 185 strains of dengue (DEN) virus types 1, 2, and 4 were recovered from febrile United States and other United Nations military personnel in Haiti. We wondered whether risk factors for dengue hemorrhagic fever (DHF) existed and, if so, were DHF cases occurring among Haitian children. Dengue transmission rates were studied in 210 school children (6-13 years old) resident in Carrefour Borough, Port-au-Prince, Haiti. When sera were tested for plaque-reduction neutralizing antibodies to DEN 1-4 viruses, nearly 85% had antibodies to two or more DEN serotypes. The annual transmission rate was estimated at 30%, a rate observed in countries endemic for DHE Haitian DEN 2 isolates were genotype I, which are repeatedly associated with DHF cases in Southeast Asia and American regions. Despite positive virologic pre-conditions, DHF cases were not recorded by experienced Port-au-Prince pediatricians. These observations, which are reminiscent of those in Africa, provide further evidence of a dengue resistance gene in black populations.