Prostatic specific antigen (PA) level was determined with a Wako test kit (Japan) for prostatic cancer and others. The incidence of abnormal values of PA in untreated prostatic cancer, was 50, 50, 80, and 100% for stage A1, C (pN0, NX), D1 and D2 cancers, respectively. Grade was not related to the level of PA. Prostatic hypertrophy, prostatitis and urinary stone showed a false positive rate of 52, 18 and 0%, respectively. The level of PA was not correlated to those of prostatic acid phosphatase (RIA). In 31% of the cases, the elevated PA decreased 4 weeks after start of endocrine treatment. Elevated PA in low grade cancer was not normalized as much as that in high and moderate grade cancers. The positive rate of PA in the serum of reactivated patients was significantly higher than that of the patients with cancer under good control by endocrine treatment.