At the end of 1984 a collaborative survey was carried out to determine the prevalence of infection with human T cell lymphotropic virus type III/lymphadenopathy associated virus (HTLV-III/LAV) and HTLV-I among 584 recipients of various blood products in Britain at that time. In 204 cases yearly point prevalence figures for infection were also obtained for 1978 to 1983. In 1984, 215 of 315 patients (68%) who had received commercial concentrate for haemophilia A were identified as positive for anti-HTLV-III/LAV as compared with only 18 of 166 patients (11%) given British concentrate alone for this disease. This difference was further emphasised by the yearly point prevalence rates: seroconversion began in 1980 among recipients of commercial concentrate, but not until 1983 did such an instance occur among recipients of British concentrate. Any conclusions must remain speculative, but possibly seropositivity among haemophiliacs may not carry so grave a prognosis as previously thought.