In 5-7% of all cases of congenital adrenogenital hyperplasia (AGH) there is 11 beta-hydroxylase deficiency (11 beta-HM). Its clinical picture is characterised by hyperandrogenism and, in some cases, arterial hypertension. The diagnosis of the enzyme deficiency depends on a reliable method of analysing the hormone in plasma and urine. As little is known and data often contradictory about the pattern of urinary steroid excretion in 11 beta-HM, these steroid metabolites were measured by a highly specific method. The pattern of urinary excretion of steroids was determined by gas chromatography and mass spectrometry (GC/MS) in 16 children and adults (11 males, 5 females: mean age 9(8)/12 [2/12-20(3)/12] years) with 11 beta-HM. In all patients there was greatly increased excretion of tetrahydrated (TH) and hexahydrated (HH) metabolites of 11-desoxycortisol (S) and desoxycorticosterone (DOC). The excretion of THS and THDOC was extremely increased in all patients. The metabolites 5 alpha-THS as well as 20 alpha- and 20 beta-isomers of HHS, not normal found in healthy persons, were present in 15 patients (94%), while the 20 alpha- and 20 beta-isomers of 5 alpha-HHS were demonstrated in 14 (88%). For the first time, 20 alpha- and 20 beta-isomers of 5 alpha-HHS were shown to be typical urinary steroid metabolites in 11-HM. The excretion of cortisol metabolites is typically decreased in 11 beta-HM. No corticosterone metabolites were found. The urinary steroid excretion pattern, measured by GC/MS, is a noninvasive, highly specific and nonselective method in the differential diagnosis of abnormal steroid metabolism.