Four children with 11 beta-hydroxysteroid dehydrogenase deficiency are described. All patients had severe hypertension, hypokalaemia, and low plasma aldosterone and renin activities. Two of the patients were siblings and two were unrelated. The most noticeable biochemical feature of these individuals was the extremely low excretion of cortisol metabolites containing an 11-carbonyl group compared to the excretion of the 11 beta-hydroxyl containing metabolites. Although this condition is readily diagnosed in affected individuals by urinary steroid analysis, carriers of the defect do not differ from normal in their urinary steroids. Both parents of the affected siblings had normal 11-oxo-steroid/11 beta-hydroxysteroid ratios under baseline conditions and the lesions could not be revealed by ACTH administration.