21-Hydroxylase congenital adrenal hyperplasia (21-OHCAH) involves a primary defect of the adrenal gland and a secondary involvement of ACTH secretion. The responses of the pituitary-adrenal axis to ovine CRH (oCRH, 1 micrograms/kg) were examined in subjects with different degrees of 21-OH deficiency. We studied 43 subjects: 7 classical and 6 nonclassical (NC) 21-OHCAH patients, 15 heterozygotes (HT) and 15 control subjects. Baseline plasma ACTH levels were higher in classical CAH than in NC-CAH, HT, and control subjects (mean +/- SEM, 66 +/- 14, 6 +/- 1.6, 4 +/- 0.5, and 5 +/- 0.5 pmol/L, respectively). The mean plasma ACTH response to oCRH in NC-CAH (17 +/- 3 pmol/L) was higher than in controls and HT (9 +/- 0.8 and 11 +/- 1.5 pmol/L). The highest ACTH responses to oCRH were obtained for classical CAH patients (126 +/- 29 pmol/L). Plasma cortisol rose after oCRH in control, HT, and NC-CAH patients but did not change in classical CAH. After oCRH, plasma 17-hydroxyprogesterone (17-OHP) were 4 +/- 0.5, 8 +/- 1.6, 93 +/- 28, and 359 +/- 110 nmol/L for controls, HT, NC-CAH, and classical patients, respectively. There was a significant correlation (r = 0.70) between 17-OHP and the ACTH responses to oCRH. The 17-OHP responses to oCRH were also correlated (r = 0.94) with the 17-OHP responses to the synthetic ACTH test. We conclude that the release of endogenous ACTH by oCRH result in graded 17-OHP responses on 21-OH deficiency. The present study also suggests that different degrees of adrenal biosynthetic defect may result in graded ACTH responses to oCRH.