Studies will be conducted in the follicular phase in controls and during amenorrhea in PCOS women. All subjects will undergo a modified frequently-sampled intravenous glucose tolerance test (FSIGTT). Glucose in the form of a 50% solution (0.3 g/kg) and regular human insulin (0.03 units/kg) will be injected through an intravenous line at 0 and 20 min, respectively. Blood will be collected at -20, -15, −5, 0, 2, 4, 8, 19, 22, 30, 40, 50, 70, 90, and 180 min for glucose and insulin determinations. Mathematical modeling of serial glucose and insulin determinations will calculate: insulin sensitivity index (SI, i.e. the action of insulin to accelerate glucose uptake and suppress glucose production), glucose effectiveness index (SG, i.e. the combined effect of glucose to enhance glucose uptake and suppress endogenous glucose production at basal insulin levels) and the acute response to glucose (AIRG).