Several distinct groups of subjects at high risk to develop noninsulin-dependent diabetes mallitus (NIDDM) have been found to have insulin secretory defects when beta-cell function is assessed in the context of peripheral insulin sensitivity. We investigated this with a modified frequently sampled iv glucose tolerance test to determine acute insulin responses to glucose (AIRg) as well as insulin action by minimal model analysis in 28 women with polycystic ovary syndrome (PCOS; 15 obese and 13 nonobese) and 29 age- and weight-matched normal women (14 obese and 15 nonobese). No subject, PCOS or control, had fasting hyperglycemia, but seven PCOS women (six obese and one nonobese) had impaired glucose tolerance or NIDDM. The PCOS women had significantly decreased insulin sensitivity compared to the normal women (P < or = 0.001), and the obese women were less sensitive than the nonobese women (P < or = 0.001). The empiric measure of insulin release, AIRg, was significantly increased by obesity (P < or = 0.01), but not by PCOS. However, the disposition index (insulin sensitivity x AIRg) was significantly decreased by both PCOS (< or = 0.005) and obesity (< or = 0.005), suggesting that AIRg was inadequate for the degree of insulin resistance. When the PCOS women with impaired glucose tolerance or NIDDM were removed from the analysis, all of the reported PCOS-related changes in insulin action and secretion remained significant. We conclude that both obese and nonobese PCOS women have beta-cell dysfunction as well as insulin resistance. However, this was not associated with glucose intolerance in the majority of PCOS women.