Insulin resistance (IR) in polycystic ovary syndrome (PCO) has been linked to hyperandrogenism and elevated luteinizing hormone (LH) levels. Fourteen patients with idiopathic hirsutism (IH), 13 with PCO, and 6 control subjects were investigated for assessment of the effects of serum LH, peripheral tissue androgens, and sex hormone-binding globulin (SHBG) on fasting immunoreactive insulin (IRI) levels. Serum LH, dehydroepiandrosterone sulfate, dihydrotestosterone, and 3 alpha-androstanediol, SHBG, and unbound testosterone (uT) were measured. Serum testosterone (T) showed a positive correlation with IRI (P less than 0.05), and SHBG showed a negative correlation (P less than 0.02). Unbound T showed a highly significant positive correlation (P less than 0.001), whereas dehydroepiandrosterone sulfate, dihydrotestosterone, and 3 alpha-androstanediol did not correlate. Gonadotropin-releasing hormone, administered to patients with IH, raised LH levels but did not change IRI levels. Spironolactone did not affect T or IRI in patients with IH but significantly lowered T and IRI in patients with PCO. It is suggested that IR is not related to LH or peripheral androgen metabolism but highly correlated with uT and SHBG, thus coupling two important factors in IR, obesity and the androgen level.