Using stable isotope dilution/gas chromatography-mass spectrometry, we determined the plasma concentrations of 5 alpha-androstane-3 alpha,17 beta-diol (AD) and 5 alpha-androstane-3 alpha,17 beta-diol-glucuronide (ADG) in 20 patients with premature pubarche (16 patients with idiopathic premature pubarche, 4 patients with late onset 21-hydroxylase deficiency) and in 55 healthy children with Tanner stages P1 to P4. No differences between sexes were found in healthy children with Tanner stages P1 and P2. Patients with idiopathic premature pubarche (median, range, nmol/1: 0.22; 0.12-0.31) or late onset 21-hydroxylase deficiency (0.27; 0.23-0.29) had higher plasma AD concentrations than healthy prepubertal children (0.09; 0.00-0.17). Regarding ADG, patients with idiopathic precocious puberty (1.35; 0.25-4.74) or late onset 21-hydroxylase deficiency (4.01; 3.50-4.58) had also higher plasma concentrations than healthy prepubertal children (0.35; 0.00-0.75). Thus, AD and ADG, which both represent end metabolites of peripheral androgen metabolism, can be regarded as markers of androgenicity. Steroid analysis by mass spectrometry is recommended, whenever uncertainties of immunological determinations are to be avoided.