We compared the values obtained by double-antibody radioimmunoassay (RIA) and immunoenzyme assay (IEA) for measuring the prostatic acid phosphatase (PAP) in human serum. Mean PAP value of IEA in normal persons was 0.582 +/- 0.228 ng/ml (M+2SD, 1.038 ng/ml). Correction of two methods in benign prostatic hypertrophy (BPH) and prostate cancer patients was excellent [r = 0.9504, Y (IEA) = -0.4378 + 0.6529X (RIA)]. False positive cases were two by IEA and one by RIA in BPH patients.