Acute exercise promotes raised HDL cholesterol concentrations by lipolysis stimulation, but this effect is insufficient to explain the more permanent HDL increases seen during regular exercise. During training periods in a group of marathon runners, we measured lipid transfer protein I (LTP-I)-mediated cholesteryl ester transfer activity (CETA) and its relationship to their HDL concentrations. Runners of both sexes showed significantly lower CETA values than those of sedentary controls. Male runners also had significantly lower serum concentrations of triglyceride, VLDL cholesterol and apolipoprotein B, and significantly higher concentrations of HDL cholesterol and apolipoprotein A-I than male controls. Results indicate that regular practice of aerobic exercise promotes modifications of lipoprotein metabolism related not only to lipolysis, but also to lower CETA. Such modifications are associated with reduced risk of atherosclerosis.