Serum prostatic acid phosphatase (PAP), gamma-seminoprotein (gamma-Sm), and prostate-specific antigen (PA) levels were measured in 63 untreated patients with prostatic cancer. The sensitivities of PAP, gamma-Sm, and PA as markers of malignancy were 68%, 83%, and 77%, respectively. The latter two markers were more sensitive than PAP, especially in stage B disease. The specificities of PAP, gamma-Sm, and PA were 95%, 93%, and 93%, respectively. Patients with multiple positive markers were very likely to have prostatic cancer. In reactivation of the disease, positive rates for gamma-Sm and PA were higher than for PAP, indicating that the former two markers are more reliable for monitoring prostatic cancer.