The purpose of this work was to investigate the relationship of gonadotropin levels to body weight and insulin levels in woman with polycystic ovary syndrome (PCOS). Specifically, we wished to test the hypothesis that circulating luteinizing hormone (LH) and insulin levels are different in obese and normal weight patients with PCOS. The basal plasma levels of gonadotropins, estrogens, androgens and sex hormone-binding globulin, the gonadotropin responses to gonadotropin releasing hormone (GnRH) and the insulin and C-peptide responses to a 3-hour oral glucose tolerance test (OGTT) were measured in 19 obese and 19 normal weight patients with PCOS and 7 obese and 8 normal weight ovulatory controls. Data of the patients were evaluated according to body weight (obese vs normal weight) and basal LH (high vs normal). There was no significant difference in basal LH and androgen levels and in the insulin response to oral glucose between obese and normal weight patients with PCOS. Compared to the weight matched controls, both obese and non obese patients showed significantly higher LH responses to GnRH and C-peptide responses to OGTT. When the high LH patients (no = 18) were compared those with normal LH (no = 20), the high LH subjects exhibited significantly higher androstenedione levels. Both obese (no = 10) and normal weight (no = 8) patients with high LH showed significantly greater C-peptide responses to OGTT than obese (no = 9) and non obese (no = 11) patients with normal LH. However, as compared with the weight matched controls, both the high LH and normal LH patients had significantly greater C-peptide responses to OGTT. We conclude that obese and non obese patients with PCOS do not seem to differ in the prevalence of elevated LH levels or in the LH secretory pattern. Insulin resistance, expressed by an enhanced pancreatic sensitivity to oral glucose, is present in both the high LH and the normal LH subjects, even though the PCOS patients with elevated LH tend to be more insulin resistant and hyperandrogenic than the normal LH patients.