The performance of two HIV antigen enzyme immunoassays (EIAs), the HTLV-III antigen EIA (Abbott) and the Innotest HIV antigen EIA (Innogenetics), was assessed using 276 HIV-1 antibody positive and 42 HIV antibody negative sera from European and African individuals. On the initial screening 16% (51/318) of the sera were reactive in the Abbott EIA and 21.4% (68/318) in the Innotest EIA. The Innotest detected significantly more confirmed HIV antigen positive sera (55/58, 94.6%) than the Abbott EIA (41/58, 70.7%). The presence of free detectable HIV antigen in African and European sera was strongly associated with the clinical classification CDC IV and with low p24 antibody levels.