Women with polycystic ovary syndrome (PCOS) are often insulin resistant and have chronic low-level inflammation. The purpose of this study was to determine the effects of hyperglycemia in vitro on tumor necrosis factor (TNF)-alpha release from mononuclear cells (MNC) in PCOS. Twelve reproductive-age women with PCOS (six lean, six obese) and 12 age-matched controls (six lean, six obese) were studied. Insulin sensitivity (IS(HOMA)) was estimated from fasting levels of glucose and insulin and percent truncal fat was determined by dual energy absorptiometry (DEXA). TNFalpha release was measured from MNC cultured under euglycemic and hyperglycemic conditions. IS(HOMA) was higher in obese women with PCOS than in lean women with PCOS (student's t-test; 73.7 +/- 14.8 vs 43.1 +/- 8.6, P < 0.05), but similar to that of obese controls. IS(HOMA) was positively correlated with percent truncal fat (r=0.57, P < 0.04). Obese women with PCOS exhibited an increase in the percent change in TNFalpha release from MNC in response to hyperglycemia compared with obese controls (10 mM, 649 +/- 208% vs 133 +/- 30%, P < 0.003; 15 mM, 799 +/- 347% vs 183 +/- 59%, P < 0.04). The TNFalpha response directly correlated with percent truncal fat (r=0.45, P < 0.03) and IS(HOMA) (r=0.40, P < 0.05) for the combined groups, and with plasma testosterone (r=0.60, P < 0.05) for women with PCOS. MNC of obese women with PCOS exhibit an increased TNFalpha response to in vitro physiologic hyperglycemia. MNC-derived TNFalpha release may contribute to insulin resistance and hyperandrogenism, particularly when the combination of PCOS and increased adiposity is present.