Thirty-six transvesical or transurethral prostatectomy cases were selected from the histopathology files of the Laiko General Hospital. Among the 36 cases, there were 10 with benign prostatic hyperplasia (8 patients having distinct areas of adenosis) and 26 cases of prostatic adenocarcinoma (6 grade I, 13 grades II and III and 7 grade IV carcinomas). From each case, silver-binding nucleolar organizer regions (AgNORs) have been counted in sections of routinely processed paraffin-embedded tissue blocks. The mean AgNOR count per case was calculated. For the cases of prostatic hyperplasia, the mean AgNOR count was found to be 2.95 +/- 0.42, for adenosis 3.45 +/- 0.56, for grade I adenocarcinoma 4.97 +/- 0.74, for grades II and III 7.31 +/- 0.81 and for grade IV adenocarcinomas 11.41 +/- 1.68. This difference in the mean AgNOR count was found to be of statistical significance (p < 0.001) between adenosis and grade I adenocarcinomas and between grade II and III and grade IV adenocarcinomas. It appears that AgNOR counting may prove to be of benefit in differentiating between some benign and malignant prostatic lesions and that it might provide information concerning the biological behavior of prostatic adenocarcinomas.