To assess the correlations between clinical and biological stages of HIV infection and HIV isolation, peripheral blood mononuclear cells from 389 HIV-infected patients were studied by 30-day cocultures with normal lymphocytes. HIV isolation was successful in 279/389 patients (71.7%). Positive isolation was more frequent in CDC IV cases (82%) than in CDC II and III cases (63.6% and 78.4% respectively). There was a close correlation between culture positivity and serum beta 2-microglobulin, CD4+ cell counts and serum p24 antigen. The day of peak detection of reverse transcriptase activity or peak p24 antigen in coculture supernatants was selected as a coculture kinetic parameter. The day of peak detection of HIV in culture occurred earlier in CDC IV cases than in CDC II and III cases, and was a prognostic factor in AIDS progression at 2 years. These data suggest that in vitro parameters related to both viral burden and replicative capacity of HIV isolates are relevant indicators of disease progression.