Plasma testosterone and 17-ketosteroids (androstenedione and dehydroepiandrosterone),as well as an index of the unbound testosterone concentration, were assayed in 7 girls with the appearance of sexual hair as an isolated phenomenon. Six had elevation of dehydroepiandrosterone sulfate, accompanied by parallel but slight increases in unbound testosterone into the low adult female range. This pattern of plasma androgens differed from that seen after ACTH stimulation prepubertally and suggests that these children were undergoing premature production of pubertal adrenal 17-ketosteroids. Dexamethasone suppression was undertaken in one child; the results indicated the production of androgens to be ACTH dependent. One child had no detectable abnormality of plasma androgens.