Exercise has beneficial effects on lipoproteins. Little is known about how long the effects persist with detraining or whether the duration of benefit is effected by training intensity or amount. Methods: Sedentary, overweight subjects (n=240), were randomized to six-month control or one of three exercise groups: 1) High-amount/vigorous-intensity; 2) Low-amount/vigorous-intensity, or 3) Low-amount/moderate-intensity. Training consisted of gradual increase in amount of exercise followed by six-months of exercise at prescribed level. Exercise included treadmill/elliptical trainer/stationary bicycle. The number of minutes necessary to expend the prescribed kcals/wk (14 kcal/kg bodyweight/wk for Low-amount groups, 23 kcal/kg/wk for High-amount group) was calculated for each subject. Average adherence (83-92%), minutes/week (207,125,203) sessions/week (3.6, 2.9, 3.5) for High-amount, Low-amount/vigorous intensity and Low-amount/moderate-intensity. Plasma was obtained at baseline, 24 hours, 5 days and 15 days after exercise cessation. Results: Continued inactivity resulted in significant increases in Low Density Lipoprotein (LDL) particle number, small dense LDL, and LDL-cholesterol. A modest amount of exercise training prevented this deterioration. Moderate, but not vigorous-intensity exercise, resulted in a sustained reduction in Very Low Density Lipoprotein (VLDL)-triglycerides over 15 days of detraining (P< 0.05). The High-amount group had significant improvements in High Density Lipoprotein (HDL)-cholesterol, HDL particle size and large HDL levels that were sustained for fifteen days after exercise stopped. Conclusion: Physical inactivity has profound negative effects on lipoprotein metabolism. Modest exercise prevented this. Moderate, but not vigorous, intensity exercise resulted in sustained VLDL-triglyceride lowering. Thirty minutes per day of vigorous exercise, like jogging, has sustained beneficial effects on HDL metabolism.