A new automated microparticle enzyme immunoassay (MEIA) for the AxSYM instrument developed recently by Abbott Laboratories was compared with two established assays, i.e. HIV-1/HIV-2 3rd Gen. Plus EIA (Abbott, Delkenheim, FRG) and Wellcozyme HIV 1 + 2 (Murex Diagnostics, Dartford, England) devised for the detection of human immunodeficiency virus type 1 (HIV-1) and HIV-2 antibodies. A total of 7293 serum samples were tested by the AxSYM HIV-1/HIV-2. The test panel included seroconversions (n = 22), samples from HIV-1 and HIV-2 positive individuals, hospitalized patients, blood donors, high risk individuals. To challenge further the specificity of the assays, large numbers of EIA repeatedly reactive but Western blot negative samples, potentially cross-reactive sera, Western blot indeterminate specimens and samples from pregnant women were tested. In four seroconversion panels, HIV-1 infection was detected one bleed earlier with the AxSYM HIV-1/HIV-2 than with the Abbott HIV-1/HIV-2 3rd Gen. Plus EIA. Although the AxSYM HIV-1/HIV-2 was tested with a higher number of challenging sera than the alternative assays, the specificity was very high (99.4%). The highest number of false positive results was obtained with serum samples that were repeatedly reactive in EIAs different from those compared in the present study. The automated AxSYM system permits the testing of a large sample number in a rapid turn-around time and by random access urgent tests can be carried out even when an assay is in progress.