Plasma carcinoembryonic antigen (CEA) determinations were carried out by the method of Hansen on 100 successive male patients admitted to the urologic service. CEA levels were elevated (above 2.4 ng/ml) in 4 of 14 patients with prostatic carcinoma, 2 of 8 patients with other malignant diseases (1 patient with cancer of the cecum and 1 patient with cancer of the bladder) and in 2 patients with non-malignant urologic disease. Neither of the latter 2 had elevated acid phosphatase. 16 patients with malignant disease were CEA negative. CEA was elevated only in patients with advanced lesions. The serum CEA test as presently constituted, is probaly no better than acid phosphatase in the diagnosis of prostate carcinoma. However, since it may pick up other malignant lesions and some prostatic carcinomas not diagnosed by acid phosphatase, it may have a place in the office diagnosis of cancer of the prostate. More prospective studies are indicated.