Sera from homosexuals and hemophiliacs in Germany were examined for antibodies to human T-lymphotropic retrovirus type III (HTLV-III) by an enzyme-linked immunosorbent assay (ELISA) against purified virus. ELISA positive sera were used to search by immunoprecipitation for HTLV-III related antigens in a persistently infected human T-cell line. A glycopolypeptide with a mol. wt. of 100 000 was regularly recognized by all positive sera. In analogy to glycosylation and high antigenicity of envelope polypeptides of other mammalian retroviruses, gp 100 seemed to be related to the env gen. Two polypeptides with mol. wts. of 24 000 and 22 000 probably representing viral core polypeptides were additionally detected by sera with high ELISA titers.