Hexosaminidase activity in prostatic tissue has been compared in 15 patients with benign prostatic hyperplasia and 15 patients with prostatic carcinoma. The ratio of enzymatic activity for the two substrates tested (p-nitrophenyl-2-acetamido-2-deoxy-β-D-glucopyranoside and p-nitrophenyl-2-acetamido-2-deoxy-β-D-galactopyranoside) was not significantly different in the two groups of patients. The proportion of hexosaminidase represented by the B isozyme was not significantly different for the two groups of patients. Prostatic tissue hexosaminidase was greater (p = 0.0141) in carcinomatous prostates than in hyperplastic prostates. © 1982, American Association for Cancer Research. All rights reserved.