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. Sedentary, overweight subjects (n = 240) were randomized to 6-mo control or one of three exercise groups: 1) high-amount/vigorous-intensity exercise; 2) low-amount/vigorous-intensity exercise; or 3) low-amount/moderate-intensity exercise. Training consisted of a gradual increase in amount of exercise followed by 6 mo of exercise at the prescribed level. Exercise included treadmill, elliptical trainer, and stationary bicycle. The number of minutes necessary to expend the prescribed kilocalories per week (14 kcal x kg body wt(-1) x wk(-1) for both low-amount groups; 23 kcal x kg body wt(-1) x wk(-1) for high-amount group) was calculated for each subject. Average adherence was 83-92% for the three groups; minutes per week were 207, 125, and 203 and sessions per week were 3.6, 2.9, and 3.5 for high-amount/vigorous-intensity, low-amount/vigorous intensity, and low-amount/moderate-intensity groups, respectively. Plasma was obtained at baseline, 24 h, 5 days, and 15 days after exercise cessation. 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-intensity 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 15 days after exercise stopped. In conclusion, physical inactivity has profound negative effects on lipoprotein metabolism. Modest exercise prevented this. Moderate-intensity 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.