In this cross-sectional study, runners and sedentary men and women were measured for lipoprotein cholesterol, triglycerides, polyacrylamide gel electrophoresis of HDL and low-density lipoprotein subclasses, apolipoproteins A-I and B, intravenous fat clearance rate, post-heparin lipoprotein lipase and hepatic lipase, adipose tissue lipoprotein lipase, cholesteryl ester transfer activity, diet, percent body fat, and regional adiposity. It was hoped that the survey would confirm or reject the weight set-point hypothesis, provide a possible explanation of the lipoprotein differences between male and female runners, and elucidate the mechanism for the lipoprotein changes that occur during exercise-induced weight loss.