Steroid excretion in urine of 12 infants with virilising adrenal tumours has been determined using gas chromatography. In six children, (Group A, five female, one male) aged 2.8-5.3 years, very high urinary excretions of 17 oxosteroids (greater than 40 mumol/24 h) were largely accounted for by dehydroepiandrosterone (DHA). In one of the girls, the pattern of steroids excreted in urine was similar to that of newborn infants, with high excretions of 16-oxygenated derivatives of DHA. The histology of this tumour suggested a neoplasia of fetal-type adrenocortical cells. Very large tumours were found in three of the infants, two of whom have died and one has multiple metastases. From the other three children, small, well-encapsulated adenomas were successfully removed. Six children (Group B), had moderately elevated 17-oxosteroid excretions (8-17 mumol/24 h). In five of these cases (four female, one male) aged 0.8-5 years, 11 beta-hydroxyandrosterone was a consistently prominent urinary steroid. In one boy, aged 7.7 years, 17-oxosteroid excretion was 15 mumol/24 h and the major steroids in urine were metabolites of pregnenolone. These six children have survived with no clinical evidence of recurrent tumour. The in vivo functional activities of the tumours can be deduced from the different profiles of steroids in urine. These have revealed heterogeneous patterns of steroid biosynthesis.