Abstract.The results obtained in a multicentre clinical trial of an enzyme immunoassay (EIA) method for hepatitis B surface antigen (HBsAg) (65,451 sera tested) have demonstrated that this new test has a significantly higher sensitivity than a reversed haemagglutination test (rHA). In a part of the trial, EIA was also compared with radioimmunoassay (RIA). Only a small number of discrepant results was obtained with these two tests, indicating similar sensitivities. No definite conclusion about a difference in sensitivities could be drawn from these results. Although the specificity of the EIA screening test is lower than that of rHA and RIA, the mean percentage of false positives was 2.2% of the total number of donor samples screened. Presumptive positives in EIA were subjected to a confirmatory test based on neutralization with human antibodies to HBsAg. After elimination of false positives in EIA screening, there was excellent agreement between EIA and RIA results.