Twenty five patients (10 males and 15 females) aged 0-23 yr with congenital adrenal hyperplasis due to 11 beta-hydroxylase deficiency were studied. They were divided into 13 classic (group A), and 12 mild (group B) patients. The patients of group A were diagnosed at a younger age and had more severe clinical symptoms (ambiguous genitalia in girls, pseudoprecocious puberty in boys). Two had neonatal salt wasting before treatment, and one gynecomastia. Seven had moderate to severe hypertension. Their mean 3 alpha,17,21-trihydroxy-5 beta-pregnan-20-one (THS) and 3 alpha, 21-dihydroxy-5 beta-pregnane-11,20-dione (THDOC) excretion was 14.2 +/- 4.1 and 7.2 +/- 4.2 mg/m2 . day, respectively. The patients of group B had mostly late onset of symptoms (hirsutism, amenorrhea in girls, pseudoprecocious puberty in boys, tall stature, and advanced bone age in both sexes). One boy had bilateral cryptorchidism. Four had moderate hypertension. In seven patients, THS (5.3 +/- 2.3 mg/m2 . day) and THDOC (3.9 +/- 0.5 mg/m2 . day) responded to ACTH. In five, only THS (4.3 +/- 1.1 mg/m2 . day) responded, but THDOC remained undetectable. It is concluded that the clinical and biochemical expression of 11 beta-hydroxylase deficiency is variable, that hypertension in not directly related to deoxycorticosterone, and that, regardless of the intensity of the defect, there are patients in whom the 11 beta-hydroxylation of 17 alpha-hydroxylated steroids only is impaired, and others in whom both the conversion of 17,20-dihydroxy-4-pregnene-3,20-dione and deoxycorticosterone are reduced.