Adrenal delta5-3beta-hydroxysteroid dehydrogenase (delta5-3beta-HSD) activity and serum corticosterone level were significantly higher in rats fed with 5% casein or 4% albumin diets after 1 hr of ether anaesthetic stress as compared to the controls, 5% casein and 20% casein (equivalent to 4% albumin) respectively. Ether anaesthesia to 20% casein fed rats caused no change in adrenal delta5-3beta-HSD activity and serum corticosterone level when compared with controls fed 20% casein diet. The results suggest that high milk protein diet may prevent acute stress effects by protecting adrenocortical activity. The present investigation opens up a new area of management of stress.