In order to provide a simple and specific assay for the detection and quantitation of IgG and IgM anti-HLA antibodies in sera, HLA antigens purified from a pool of 240 random donor platelets were used to develop a solid-phase enzyme-linked immunoassay (EIA). The reference values for identifying the presence of IgG or IgM anti-HLA antibodies were determined by assaying sera from 39 healthy individuals without prior HLA alloimmunization. The assay was evaluated by studying sera from 122 patients who had been characterized previously for panel reactive antibodies by the lymphocytotoxicity assay (LCA). A significant linear correlation between two assays was noted (r = 0.8, P = 0.0001). Further analyses of the data demonstrated that the newly developed EIA has 100% specificity and 95.3% sensitivity as compared with the LCA. Additional studies revealed that patients whose PRA increased or decreased over time were in parallel with antibody levels measured by EIA. When the EIA was used to measure anti-HLA antibody titers, it was more sensitive than the LCA. Since the EIA is sensitive, specific, and technically less demanding, it should provide an useful alternative to reduce the number of the more laborious panel studies for monitoring anti-HLA antibody status in candidates for organ transplantation and recipients of blood transfusions.