Abstract
1 Both the circadian and stress-induced changes in plasma corticosterone concentration were abolished by the inclusion of betamethasone in the drinking water of rats. 2 Adrenal sensitivity to exogenous corticotrophin (ACTH) was unimpaired by the betamethasone treatment. 3 The normal circadian rhythm in plasma corticosterone returned within 1 day of withdrawal of the steroid, but the response to stress was normal only after 3 days. 4 The possible significance of these observations is discussed.