11 patients with 21-hydroxylase deficiency were treated with three different corticosteroids and two different distributions of therapy during daytime. We found that: 1) a higher dose of steroid in the evening had a markedly inhibitory effect on nocturnal GH secretion; 2) of the steroids we used, dexamethasone caused the greatest reduction in nocturnal GH secretion; 3) in this study adrenal hormones seem less influenced by the different distribution of the corticosteroids during the 24 hours period.