The prevalence of HIV-antibody was studied in a cohort of 156 haemophiliacs controlled since before 1986. Ninety four patients (60%) were HIV-seropositive, and all of them had been previously treated with non-heated factor concentrates. Seroprevalence was 50% by 1983. Evidence for previous negative results was only available in 19 seropositive patients and all of them seroconverted before 1985. For the 148 patients exposed to non-heat treated factor concentrates, severe haemophiliacs and those with factor consumption greater than 100 x 10(3) had the maximal rate of seropositivity (81% and 75% respectively, p less than 0.005). Fifteen patients developed AIDS (10% of the HIV-positive), 12 of which have died. HIV infection has a high prevalence and it has become the most important cause of death in our haemophiliacs.