1 The half-life of hydrocortisone (cortisol) has been measured in six patients before and after a three-week course of prednisone given for asthma. 2 There was considerable variation in peak plasma level of cortisol both within and between patients, but on both occasions the plasma half-lives were the same. 3 It was concluded that short courses of prednisone have no effect on the handling of hydrocortisone.