Nicotinic acid has favorable effects on atherogenic dyslipidemia. However, in some patients who have diabetes, crystalline nicotinic acid decreases glycemic control; this effect could be due to a marked rebound of nonesterified fatty acids (NEFAs) observed after nicotinic acid suppression of lipolysis in adipose tissue. Recent reports have indicated that small doses of extended-release nicotinic acid do not cause a substantial decrease in glucose levels. Therefore, in this study, we examined whether 2 g/day of extended-release nicotinic acid abolishes the NEFA rebound that is reported with crystalline nicotinic acid. Seventeen men who had the metabolic syndrome (8 did not have type 2 diabetes and 9 did) were treated for 4 months. At baseline and at 4 months, measurements were made of plasma glucose, insulin, and NEFA during an oral glucose tolerance test. At 3 months, effects of extended-release nicotinic acid on NEFA levels and flux rates were determined on 3 separate days at 3 separate intervals after the final dose of nicotinic acid (4, 9, and 28 hours). Values obtained at 28 hours were taken as baseline (i.e., no nicotinic acid remaining in the circulation). After 4 hours (percent baseline), NEFA levels were -30% without diabetes and -37% with diabetes, and flux rates were -21% without diabetes and -25% with diabetes; after 9 hours, NEFA levels were 43% without diabetes and 50% with diabetes, and flux rates were 38% without diabetes and 70% with diabetes. Extended-release nicotinic acid did not abolish NEFA rebound. Nonetheless, the rebound was much less than previously reported for crystalline nicotinic acid. Moreover, after 4 months of nicotinic acid therapy, levels of NEFA, glucose, and insulin during the oral glucose tolerance test were not significantly different from those before institution of nicotinic acid therapy, suggesting minimal changes in insulin sensitivity.