Using a combined infusion of somatostatin, insulin and glucose, insulin resistance was assessed in vivo in two groups of females with polycystic ovaries (PCO), obese (PB-PCO) and normal weight (NO-PCO) and in two groups of matched (for age, sex and body mass index) controls (OB and NO). A steady state plasma glucose (SSPG) and insulin (SSPI) was attained after 90 min. OB-PCO and NO-PCO showed higher SSPG with respect to matched controls. The SSPG levels were related to body mass index (r = 0.69; P less than 0.001). The SSPG values were significantly correlated with the fasting insulin levels (r = 0.47; P less than 0.003). Gonadotrophin and steroid peripheral blood concentrations were also evaluated in the PCO females. A significant correlation was found between the SSPG values and the dehydroepiandrosterone sulphate levels (r = 0.46; P less than 0.05) and between the fasting insulin levels and the androstenedione concentrations (r = 0.64; P less than 0.01). Moreover, significant correlation coefficients were found between the glucose to insulin ratio and the A (r = -0.59; P less than 0.01) and the DHEA-S (r = -0.50; P less than 0.05) plasma levels. Finally, no relationship between body mass index and A or DHEA-S levels was found in PCO females considered as a group. We conclude that insulin resistance is present in females with PCO and it is mainly due to the presence of obesity, but other factors such as androgen levels, probably of adrenal sources, must be considered as a cause.