In 49 patients affected by PCO syndrome the serum levels of dehydroepiandrosterone-sulphate (DHEAs) were determined and correlated with the clinical presentation and the endocrine pattern. Twenty-three patients (47%) had high DHEAs levels (h-DHEAs patients). They presented a milder clinical presentation (low incidence of amenorrhea) than PCO patients with normal DHEAs levels (n-DHEAs patients). In h-DHEAs patients the finding of a normal DHEAs response to ACTH and of slightly increased 170HP serum levels suggested that the elevation of serum DHEAs was not due to an adrenal enzymatic deficiency but to a tonic hyperstimulation of the adrenals. Two subgroups of h-DHEAs patients were identified: in the first subgroup, PRL and estrone levels were increased and probably explained the DHEAs hypersecretion; in the second subgroup, the endocrine pattern was very similar to that observed in n-DHEAs patients and a clear explanation for DHEAs increase was not found, although the possibility of an exaggerated secretion of some pituitary hormones with adrenal androgen stimulating activity must be considered.