Background: Aerobic exercise and niacin are frequently used strategies for reducing serum triglycerides, and, yet, there is no information regarding the combined effects of these strategies on postprandial triglycerides. Objective: We compared the effects of aerobic exercise and 6 wk of extended-release niacin on postprandial triglycerides in men with the metabolic syndrome. Design: Fifteen participants underwent each of 4 conditions: control - high-fat meal only (100 g fat); exercise - aerobic exercise performed 1 h before a high-fat meal; niacin - high-fat meal consumed after 6 wk of niacin; and niacin + exercise - high-fat meal consumed after 6 wk of niacin and 1 h after aerobic exercise. Temporal responses for triglyceride and insulin concentrations were measured and total (AUCT) and incremental (AUCI) areas under the curve were calculated. Differences were determined by using a 2-factor repeated-measures analysis of variance (P < 0.05 for all). Results: Exercise lowered the triglyceride AUCI by 32% compared with control (724 ± 118 and 1058 ± 137, respectively). Niacin had no influence on the triglyceride AUCI and attenuated the triglyceride-lowering effect of exercise when combined. Niacin + exercise had no effect on the triglyceride AUCI but decreased the insulin AUCI after niacin administration. Conclusions: Aerobic exercise lowers the postprandial triglyceride response to a high-fat meal. Niacin lowers fasting but not postprandial triglycerides and appears to influence the triglyceride-lowering effect of aerobic exercise when combined. However, exercise decreases postprandial insulin concentrations after niacin administration, which illustrates the potential metabolic benefits of exercise in persons taking niacin. © 2008 American Society for Nutrition.