On the basis of human immunodeficiency virus (HIV) needlestick studies, the time to seroconversion for anti-HIV antibodies is 1-9 months (mean, approximately 2-3 months). However, an earlier marker of an immune response to HIV often occurs-serum anti-HIV antibodies reactive with live HIV-infected cells, termed "early HIV antibodies." The specificities of these antibodies are characterized by the recognition of type-specific conformational epitopes of the HIV envelope glycoprotein (gp) 160 and gp41. By use of a third-generation native HIV(IIIB) gp160 enzyme immunoassay (EIA), detection of HIV antibodies occurred, on average, 33 days earlier than did detection by commercial EIA and 25 days earlier than did detection by the reference antigen and reverse-transcription polymerase chain reaction (RT-PCR) assays in 3 of 5 HIV seroconversion panels. A fourth panel possessed early HIV antibodies that reacted with HIV(213) but not with HIV(IIIB), allowing for detection of HIV antibodies approximately 3 weeks earlier than by RT-PCR or other current tests.