There are three different test generations of enzyme-linked immunosorbent assays (ELISA) for the detection of human immunodeficiency virus (HIV) infection, depending on whether virus lysate, recombinant proteins or synthetic peptides are used as solid phase antigen. Four different assays, i.e., three sandwich ELISAs and one competitive test, were used to demonstrate differences between the three systems with regard to the content of different diagnostically relevant virus proteins. The sensitivities and specificities of these assays were compared by using 312 anti-HIV positive sera and 500 sera of healthy blood donors. The highest sensitivity and specificity were achieved by the competitive ELISA based on recombinant proteins, and by the sandwich ELISA based on synthetic peptides.