The effects of a single session of moderate intensity (65% VO(2)max) aerobic exercise expending 500 kcal of energy on serum lipid and lipoprotein-cholesterol concentrations and the electrophoretic characteristics of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles were determined in 11 sedentary, eumenorrheic, premenopausal women immediately prior to, and 24 and 48 h following exercise. Repeated measures analysis of variance revealed significant reductions in triglyceride (25.0%), HDL-cholesterol (10.9%), and HDL(3)-cholesterol (11.9%) concentrations at 48 h post-exercise. Despite these changes in lipid and lipoprotein-cholesterol concentrations, no significant changes were observed in peak LDL or HDL particle sizes or in the distribution of cholesterol within the LDL and HDL subfractions. Accordingly, it appears that a single session of moderate intensity aerobic exercise expending 500 kcal (2,092 kJ) of energy promotes reductions in triglyceride, HDL-C, and HDL(3)-C concentrations without concomitantly affecting the electrophoretic characteristics of LDL and HDL particles in this sample of women.