1. The effect of dietary protein levels on the proteolytic activity in the intestines of the air-breathing fish, Clarias batrachus (Linn.) has been studied 2. Activity of proteolytic enzymes increased significantly in fishes maintained with a 50% protein diet from those maintained with a 25% protein diet; still higher dietary protein percentage showed no further stimulation of enzyme activity. 3. In a study on the determination of sub-cellular localisation, it has been found that protease activity is more prominent in lysosomes than in other organelles of the cell. 4. A sixty fold purification of alkaline protease from the intestine of Clarias batrachus has been achieved by ion exchange chromatography on DEAE cellulose which has been further checked by polyacrylamide gel electrophoresis. © 1978 Dr. W. Junk b. v. Publishers.