We have developed an enzyme-linked immunosorbent assay (ELISA) specific for antibodies to the envelope glycoproteins gp120 and gp160 of HIV-1 An antibody to a conserved epitope on gp120 is adsorbed to a solid phase and used to capture gp120 and/or gp160 from solution. This may be purified recombinant protein or in simple, non-denaturing detergent extracts of different strains of HIV-1. Human serum antibodies bound to the captured antigen are subsequently detected with an anti-human antibody coniugated to alkaline phosphatase, and the AMPAK ELISA amplification system (Novo BioLabs, Cambridge, UK). With this procedure, antibodies can be detected that recognize gp120 from a wide range of divergent HIV-1 strains. The ELISA is sufficiently sensitive to detect env antibodies in sera from HIV-positive individuals at dilutions of 1.3000 00. No repeatable false-positives were detected in a screen of 250 normal serum samples. Env antibodies were detected in all 37 strongly HIV-positive sera tested, and in four sera that were borderline or weakly positive in commercial ELISA. However, 55 sera positive in commercial ELISA but unconfirmable by Western blot (‘ambiguously’ positive) did not contain detectable env antibodies.