Since 1983 the morbidity and mortality rates as well as results of haematological, immunological and (later) HIV serological tests were recorded prospectively for 497 HIV-positive patients during 1837 clinic visits at least twice within at most six months for a median period of observation of 18 months (range 6-64 months). The rate of progression to a higher stage was calculated according to the method of Kaplan-Meier. The rate for asymptomatic patients was 16% after one and 33% after two years; for patients with persisting generalized lymphadenopathy it was 13% and 21%, respectively, for those with AIDS-related complex 28% and 47%, respectively, and for those with AIDS 33% and 82%, respectively. As for results of laboratory tests, patients with progressive disease had significantly lower titres of anti-HIV nuclear antibodies, as well as a higher incidence of HIV-p24 antigen. Haemoglobin levels, platelet and lymphocyte counts and number of CD-4-positive lymphocytes were significantly lower, Neopterin and beta 2-microglobulins higher (P less than 0.01).