Hyperandrogenism, insulin resistance, and obesity are common features of polycystic ovarian syndrome (PCOS). This study was designed to investigate the relationship among these factors and how they might contribute to ovulatory dysfunction in PCOS. Adrenal androgen secretion and insulin resistance were quantified in oligomenorrheic women with PCOS and in three groups of eumenorrheic women: weight-matched hirsute women, obese nonhirsute women, and thin nonhirsute women. Adrenal androgen secretion was defined as the androstenedione response to synthetic corticotropin. Insulin resistance was estimated by calculating the area under the curve for serum insulin levels in response to a 75 g oral glucose load. The mean serum androstenedione response (nmol/L) to corticotropin in PCOS (5.6 +/- 1.3) was greater than that in eumenorrheic hirsute women (3.4 +/- 0.5; P < 0.10), obese nonhirsute women (1.8 +/- 0.8; P < 0.05), and lean nonhirsute women (1.9 +/- 0.5; P < 0.05). The serum androstenedione response was not correlated with body mass index (BMI). The area under the curve for serum insulin (mU/L.min/1000) in PCOS (29.1 +/- 5.3) was greater (P < 0.001) than in eumenorrheic hirsute women (9.1 +/- 1.7), obese nonhirsute women (5.8 +/- 1.0), and lean nonhirsute women (4.5 +/- 0.4). The serum insulin response was highly correlated with BMI (P < 0.001) in the three groups of obese women, but women with PCOS became significantly more insulin resistant with increasing BMI (P < 0.02). There was no correlation between adrenal androgen secretion and insulin resistance in any of the groups. We conclude that adrenal hyperandrogenism and insulin resistance are independent predictors of anovulation in hirsute women. These conditions are present in both oligomenorrheic and eumenorrheic hirsute women, but are present to a greater extent in anovulatory women. Obese women with PCOS also differ from eumenorrheic controls by developing a greater degree of insulin resistance as body mass increases.