The PSA density was calculated in 98 patients with carcinoma of the prostate by using the weight and/or volume of the radical prostatectomy specimen. In 22 of 98 patients, PSA serum levels ranged between 4 and 10 ng/ml. Eleven patients showed PSA serum levels below 4 ng/ml and 65 patients above 10 ng/ml. Sixty-one of the 65 patients with PSA serum levels > 10 ng/ml had PSAD values above 0.15, and we therefore suspected the presence of carcinoma of the prostate according to Benson et al. Twelve of the 22 patients with PSA serum levels between 4 and 10 ng/ml had PSAD values below the cut-off value of 0.15. In addition, all 11 patients with PSA values < 4 ng/ml showed PSAD values < 0.15, a range that can be regarded as almost harmless according to Benson et al. In conclusion, it seems apparent that in patients with PSA serum levels < 10 ng/ml, no important additional information is obtained from the PSAD determination. Routine measurement of PSAD for evaluating the risk of carcinoma of the prostate in individual cases can therefore not be recommended.