Seminal fluid contains a number of proteinase activities, many of which are secreted by the prostate gland. Our objective was to determine proteinase activities in human prostatic secretions which can degrade gelatin and/or casein. Prostatic secretions were collected by prostate massage from men with benign prostatic hyperplasia prior to surgery to relieve obstruction. Significant proteinase activities towards gelatin of about 81, 86, 94, 111, 115 and 163 Kd as well as less active forms of 23, 36, 38, 132, 137, and 148 Kd were detected using protein substrate-polyacrylamide gel zymography. In addition, Ca2+ stimulated activities of approximately 64, 66, 71 and 76 Kd; however, EDTA and EGTA inhibited all activities but the 23, 36 and 38 Kd forms (these were inhibited by benzamidine and epsilon-amino caproic acid). This suggests that the gelatinolytic activities of 64 Kd and greater were metalloproteinases and those of 23, 36, and 38 Kd were serine proteinases. Significant caseinolytic activities of 22, 25, 35, 37, 57, 90, 96, 102 and 116 Kd were found as well as several less active forms and a 12 Kd activity stimulated by Ca2+. Caseinolytic activities of 12, 14, 16, 96, 102, 116, and 126 Kd were inhibited by EDTA and EGTA indicating they are metalloproteinases. The 35, 37, 57 and 58 Kd caseinolytic activities were inhibited by benzamidine, and the 57 and 58 Kd forms by epsilon-aminocaproic acid suggesting they were serine proteinases. There was considerable variability among individuals in the molecular forms of proteinase activity expressed as well as the level of their activity. A significant decrease in the frequency of expression of the 132 Kd gelatinolytic activity was found in secretions from men with atypia or adenocarcinoma, as compared with men with benign prostatic hyperplasia alone. Our results show that human prostatic secretion contains a variety of proteinase activities. The expression of the 132 Kd gelatinolytic activity could prove useful in further evaluation of neoplastic prostatic disease.