We propose that carcinoembryonic antigen (CEA) may be a tumor marker for prostatic cancer in addition to prostate specific antigen (PSA), gamma-seminoprotein and prostate acid phosphatase (PAP). The tests were done on 15 sera and autopsy specimens of prostatic cancer. Eight of them were clinical cancers and the remaining seven were incidental ones. We measured serum PAP, PSA, CEA and CA 19-9 and immunohistochemically evaluated these specimens. In clinical cancers, serum PAP, PSA, CEA and CA 19-9 were 1272.9 +/- 3094.4, 146.7 +/- 233.6, 36.3 +/- 36.0 and 80.4 +/- 92.0. Immunohistochemically, all were positive for PAP, PSA, CEA and CA 19-9. In incidental cancers, serum PAP, PSA, CEA and CA 19-9 were 2.4 +/- 1.5, 7.9 +/- 16.9, 128.1 +/- 182.7 and 201.8 +/- 416.1. We conclude that the patients with higher levels of plasma PAP or PSA should go through CEA and CA 19-9 measurement in order to diagnose clinical prostatic cancer.