The most reliable laboratory test for prostate cancer remains prostatic phosphatase determination. With the spectrophotometric method, however, falsely negative results are to be expected in 40% of stage D lesions. In only one third of patients with localized disease results are correctly positive. This poor specificity and sensitivity can be improved by radioimmunoassay (RIA). Using this technique the prostatogenic isoenzyme is elevated in 50% of stage A and in 80% of stage B carcinoma, suggesting RIA for screening. Erythrocyte sedimentation rate or serum iron and copper are not necessarily of prognostic value. Phosphatase determination of bone marrow aspirates also requires the RIA method if differentiation of stage C and D is to be expected. Serum hormone assays are not yet introduced into routine staging programs. Serum and urinary markers such as CEA, polyamines of LDH isoenzymes are unspecific and of uncertain value in prostatic carcinoma. Measurement of urinary hydroxyproline seems a reliable method for the search of osseous spread; other bone diseases have to be excluded. In patients with prostate cancer laboratory tests still represent adjunctive measures in connection with the clinical diagnostic armamentarium of urologists.