Summary Adrenalectomy causes significant decreases in arginase and arginine synthetase activity, but has no effect on lactic acid dehydrogenase activity. All treatments known to increase protein catabolism increased the arginine synthetase activity. The results with arginase were not as clear cut as they also appeared to be affected by losses in weight. All changes in activity of the 3 enzymes, arginine synthetase, arginase. and lactic acid dehydrogenase, observed with various treatments in intact rats were also observed in adrenalectomized animals. The author would like to thank C. H. Sodikoff, R. V. Henrickson, and E. H. Avcry for technical assistance.