Steroid sulphates such as oestrone sulphate (OE1S) and dehydroepiandrosterone sulphate (DHEAS) have been suggested to be of biological importance in different disease states such as breast cancer and atherosclerosis. Previous studies have shown that drugs such as aminoglutethimide and rifampicin that induce P450-dependent mixed-function oxygenases selectively suppress plasma OE1S levels. The aim of this study was to evaluate the influence of treatment with carbamazepine, an antiepileptic drug known to stimulate mixed-function oxygenases, on plasma levels of OE1S and DHEAS. We measured plasma OE1S and DHEAS together with other plasma oestrogens and androgens in male epileptic patients before and during carbamazepine monotherapy. Patients treated with valproate monotherapy acted as a control group. Treatment with carbamazepine decreased plasma OE1S levels from a mean value of 810.8 to 411.6 pmol/l (mean suppression to 50.7% of pretreatment levels, P < 0.001). Similarly, the ratio of OE1S to OE1 fell to 59.9% of pretreatment levels (P < 0.001)). DHEAS decreased from a mean level of 4.9 mumol/l before treatment to 3.0 mumol/l during carbamazepine therapy (mean reduction to 62.7% of pretreatment levels (P < 0.001), while the ratio of DHEAS to DHEA fell to 63.0% of pretreatment values (P < 0.01). No significant change in plasma levels of the other oestrogens or androgens measured was observed. Treatment with valproate caused a slight decrease in FSH levels (P < 0.05), but no change in any of the other hormones measured was observed. Studies are warranted to evaluate the possible effects of long-term treatment with carbamazepine on the risk of developing endocrine-sensitive tumours and cardiovascular disease and also the possible effects of alterations in plasma DHEAS on epileptic activity.