During metamorphosis, the collagen layer (basement lamella) of the resorbing tail fin of bullfrog tadpole was markedly disintegrated, and was invaded by mesenchymal cells from below, which contained cytoplasmic vacuoles enclosing collagen fibrils. Participation of the locally produced collagenase in the process was discussed.By use of the tissue incubation method, collagenolytlc activity was found In the wound tissues of the rabbit dorsal skin, and its significance In the wound healing process was discussed. Some of the repairing tissues after incubation were histologically examined.In the human stomach, high degree of collagenolytlc activity was observed in the mucosa affected by gastritis after Incubation, and there were several evidences that some kinds of cancerous tissues possessed a certain degree of the activity. The collagenolytlc enzyme from the mucosa of gastritis was proved to have the characteristics of animal collagenase, previously obtained from tadpoles or other mammalian tissues.