With the aim of evaluating the specific pattern of in vitro antibody production (IVAP) in human immunodeficiency virus type 1 (HIV-1)-infected long-term non-progressors (LTNPs), we tested 20 subjects who had remained asymptomatic for more than 8 years with a CD4+ cell count higher than 500/microliter and 59 patients at different stages of HIV-1 infection as controls. In cell cultures, IVAP was detected in 14 out of 20 LTNPs (70%), in 5 out of 6 recent seroconverters (83%), and in all the other control patients. Anti-p24 antibody production was significantly lower in LTNPs than in asymptomatic patients with a more recent infection. Recent seroconverters and patients with AIDS did not produce anti-p24 antibodies (P = 0.02). Anti-gp160 antibodies were produced by peripheral blood mononuclear cells from LTNPs in 12/20 cases. CD4+ cell count was significantly higher in IVAP-negative than in IVAP-positive LTNPs (P = 0.013), while the viral load was not significantly different. Specific anti-HIV-1 antibody production did not seem to be a correlate of long-term nonprogression.