According to published data the group of urinary total 17-ketosteroid sulfates appears to represent an index of overall adrenal androgen production, at least before the onset of puberty. To quantify total 17-ketosteroid sulfates a modified colorimetric assay based on the Zimmermann reaction was validated. 17-ketosteroid sulfates were measured without previous hydrolysis (as conjugated Zimmermann chromogens against authentic dehydroepiandrosterone sulfate (DHEAS) as assay standard) after C18 reversed-phase extraction and LH-20 chromatography. Intra- and inter-assay coefficients of variation were 8.4% (15.0%) and 5.9% (17.6%), respectively, at urinary 17-ketosteroid sulfate concentrations of 10.8 (1.9) nmol/ml. Recoveries observed in spiking and parallelism experiments varied between 88 and 102%. In a group of 4-year-old children showing a renal DHEAS output of less than 0.1 mumol/d/1.73 m2 (measured by radioimmunoassay) a relatively high median 17-ketosteroid sulfate excretion of 1.29 mumol/d/1.73 m2 was found. Older children aged 8 years as well as a group aged 12-14 years demonstrated only moderately higher urinary 17-ketosteroid sulfates whereas excretion of DHEAS/d/1.73 m2 more than tripled from age group to age group. For children from 8 years onwards, adolescents, and adults, linear regression analysis indicated that urinary DHEAS elevations seem to contribute with a constant proportion of approximately 70% to the increments of total urinary 17-ketosteroid sulfates. These findings suggest that the attainment of such a constant relationship (between the total 17-ketosteroid sulfates and their major component) from about 8 years of age onwards could represent the hormonal correlate of the completion of the continuous zona reticularis in the adrenal gland (developing around this age from a focal reticularis zone).