Androgen, oestrogen and gonadotrophin levels in patients with the polycystic ovary syndrome (PCOS) were compared with those in normal ovulatory women (controls), and were correlated with the number of microcysts in the polycystic ovaries studied. The androgen levels (testosterone, delta 4-androstenedione and dehydroepiandrosterone-sulphate), oestrogen levels (oestrone and oestrone/oestradiol-17 ratio) and gonadotrophin levels [luteinizing hormone (LH) and LH/follicle stimulating hormone (FSH) ratio] of PCOS patients were significantly higher than those of controls. The number of microcysts in polycystic ovaries was significantly correlated with androstenedione, which in turn was also significantly correlated with LH and LH/FSH ratio. These correlations may play a part in the maintenance of chronic anovulation in PCOS.