Collagenolytic activity was found to be present in various digestive organs of nineteen species of teleost. The activity was detected in the pancreas, the pyloric caeca together with the surrounding fatty tissue, the intestine, the mesentery, and the mesenteric and fatty tissue around the intestine. When considered together with the fact that the pancreatic tissue is diffuse in many teleosts, these findings suggest that collagenase originates from the pancreas. In the cases of rainbow trout and yellow-tail, collagenase was detected in the fatty tissue between the pyloric caeca rather than in the caeca themselves. These findings substantiate the theory that collagenase is of pancreatic origin, since the pancreatic tissue is embedded in the fatty tissue between the caeca. In addition, it was observed that the collagenolytic activity in the digestive system of the fishes examined could be correlated to their usual diet in nature.