The clinical significance of serum basic fetoprotein (BFP) in prostatic cancer was investigated together with serum prostatic acid phosphatase (PAP), gamma-seminoprotein (gamma-Sm) and prostate specific antigen (PA). Investigated in this study were 40 patients with prostatic cancer, ranging in age from 50 to 85 years (mean age: 69.5 years). According to clinical staging, 3 cases (7.5%) had a stage A disease, 10 cases (25.0%) a stage B disease, 7 cases (17.5%) a stage C disease, and 20 cases (50.0%) a stage D disease. The positive rates for serum BFP, PAP, gamma-Sm, and PSA were 60.0, 45.0, 63.6, and 68.4%, respectively, and these rates increased as the stage advanced. The above results suggest that BFP is the most useful marker of the four for monitoring prostatic cancer. In a combination assay of these four markers, 29 (87.9%) of 33 patients with prostatic cancer could be diagnosed by observing an elevated serum level in one of the markers. This suggests that a combination assay of BFP, PAP, gamma-Sm and PSA in patients with prostatic cancer is useful for diagnosis and monitoring of the disease.