A total of six amino acid sequences encoded in conserved regions of the HIV-env (three from gp120 and three from gp41) were selected as potential antigenic domains. These sequences (11-20 amino acids) were fused to the NH2 terminus of beta-galactosidase by recombinant DNA techniques, and the purified chimeric proteins were used to titer (by immunodots) 75 sera from HIV-infected individuals of various stages. All the HIV antigens were recognized by some or all the HIV-seropositive sera but by none of the control sera. Of the three conserved domains in gp41, two are highly immunodominant. All (100%) HIV-seropositive sera reacted with one of these immunodominant domains in titers (approximately 1:100,000) almost two orders of magnitude higher than any other tested domain. This emphasizes the diagnostic value of the epitopes (ERYLKDQLLGIWGCSGKLIC) previously (see Refs. 11 and 12) identified in this domain. A decrease in average antibody titers is observed in late stages of infection for all the antigens tested, yet distribution of antibody reactivity was independent of stage for only three of the six domains. A significantly higher proportion of reactivity of seropositive sera in early stage (62%) compared with late stage (11%) of infection was found for a domain (NVTENFNMWKN) mapped at the NH2 terminus of gp120; serum antibody reactivity with this domain also correlated with a lack of culturable HIV in blood mononuclear cells.