Marginal salt loss occurs in patients with congenital adrenal hyperplasia due to 11 beta-hydroxylase (11-OHase) deficiency treated with dexamethasone and is accompanied by increased PRA. The present study was undertaken to evaluate the effect of the stimulated renin-angiotensin system on pituitary-adrenal suppression. Seven patients with 11-OHase deficiency were subjected to a series of treatments with dexamethasone, cortisol, and combined cortisol and 9 alpha-fluorohydrocortisone. The latter combination suppressed PRA and sodium excretion, and produced better control of the pituitary-adrenal axis, as measured by plasma ACTA and serum 11-deoxycortisol. We conclude that in children with 11-OHase deficiency, PRA needs to be monitored, and when it is elevated, mineralocorticoid replacement is indicated.