1. There is a poor relationship between the circulating half-life a glucocorticoid and either its potency or its duration of action. Many actions of a glucocorticoid have unequal durations. The duration of action varies with the dose. 2. The presence of biological activity as a glucocorticoid depends on the presence of a hydroxyl group at carbon number 11. Cortisone and prednisone, which are 11-keto compounds, must be converted to 11-beta-hydroxyl compounds to be effective. This reaction may be impaired in the presence of liver disease. 3. Iatrogenic Cushing's syndrome differs from spontaneous Cushing's syndrome in several respects, possibly because in the former ACTH is suppressed but in Cushing's syndrome associated with bilateral adrenal hyperplasia ACTH levels are elevated...