We investigated the feedback inhibition of insulin and glucagon secretion during euglycemic-hyperinsulinemic clamp at about 350 pmol/l in 16 patients with abdominal obesity [8 with normal glucose tolerance (oNGT), 8 with impaired glucose tolerance (oIGT)] and 8 normal-weight subjects matched for age, sex and blood pressure. In oNGT and oIGT, fasting plasma C-peptide levels were twice those in the controls (962±51 and 915±85 vs 439±28 pmol/l,P<0.001) and="" their="" suppression="" was="" lower="" than="" in="" the="" controls,="" both="" in="" absolute="" terms="" (155±19="" and="" 185±17="" vs="" 274±18="">P<0.001) and="" as="" a="" percentage="" decline="" from="" basal="" levels="" (16±2%="" and="" 21±2%="" vs="">P<0.001). fasting="" plasma="" glucagon="" levels="" were="" similar="" in="" the="" patients="" and="" in="" the="" controls,="" but="" were="" less="" suppressed="" during="" clamp="" in="" ongt="" and="" oigt,="" both="" in="" absolute="" terms="" (7.0±0.9="" and="" 5.6±0.6="" vs="" 13.2±1.2="">P<0.001) and="" as="" a="" percentage="" change="" from="" basal="" levels="" (23±3%="" and="" 19±2%="" vs="">P<0.001). these="" results="" suggest="" that="" the="" insulin="" feedback="" on="" b="" and="" a="" cells="" is="" impaired="" in="" abdominal="" obesity,="" and="" that="" this="" defect="" is="" of="" similar="" degree="" in="" ongt="" and="" oigt.="" these="" alterations="" could="" be="" implicated="" in="" the="" pathogenesis="" of="" hyperinsulinemia="" in="">