The Gleason grading system for prostate cancer was applied quantitatively to analysis of entire tumors in 209 radical prostatectomy specimens from patients with clinical Stage A and Stage B carcinoma. Percentage of poorly differentiated tumor (Gleason histologic pattern 4 and/or 5) was related to quantitated cancer volume, cancer location within the prostate, and presence or absence of pelvic lymph node metastasis. A strong correlation was found between cancer volume, percentage of poorly differentiated cancer, and nodal metastasis. Twenty-two of 38 patients with more than 3.2 cc of Gleason histologic pattern 4-5 cancer had nodes with positive results, compared with one of 171 patients with less than 3.2 cc of pattern 4-5 cancer. Gleason histologic patterns 1 and 2 cancer was found mainly in a small subgroup of tumors whose site of origin was in the anatomic transition zone and whose volume was less than 1 cc. Gleason "cribriform" histologic pattern 3 cancer was thought to represent mainly intraductal carcinoma. Its increase in area with increasing cancer volume paralleled the increase in pattern 4 cancer and was counter to the decrease in other types of pattern 3 cancer.