The purpose of this study was to examine the effect of one bout of low-intensity exercise on the lipemic response to a high-fat meal. Twelve (six women, six men) normolipidemic adults aged 25.8 +/- 1.2 years (mean +/- SEM) took part in two trials. In the exercise trial, subjects walked for 2 hours on a treadmill at 30.9% +/- 1.6% of maximal oxygen uptake (VO2 max) 15 hours before ingestion of the test meal. In the control trial, subjects rested the day before the test meal. After a 12-hour fast, blood samples were obtained by venous cannulation before ingestion and hourly after ingestion for 6 hours. Serum was analyzed for triacylglycerol (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and HDL2-C, apolipoproteins (apos) A-I and B, free fatty acids (FFA), free glycerol, glucose, and insulin. TG values were corrected for free glycerol. Fasting serum TG and peak TG concentrations were lower (Wilcoxon, P < .05) for the exercise trial than for the control trial (0.74 +/- 0.03 v 0.92 +/- 0.08 and 1.98 +/- 0.18 v 2.59 +/- 0.32 mmol.L-1, respectively). The total lipemic response (area under the TG/time curve, normalized to the 0-hour level) was 31% +/- 7% lower in the exercise trial (4.28 +/- 0.66 v 6.46 +/- 1.08 mmol.L-1.h, P < .01). No differences were found between trials in the other parameters. These results show that a single bout of low-intensity exercise reduces the extent of postprandial lipemia in normolipidemic young adults. One possible mechanism is enhanced lipoprotein lipase (LPL) activity in the exercised skeletal muscle.