The effectiveness of endurance exercise training (without concomitant weight loss) for improving lipoprotein lipid levels in obese individuals remains controversial. The purpose of this study was to determine whether lipoprotein lipid responses to endurance exercise training are affected by obesity. Healthy middle-aged and older (57 +/- 2 years) lean (n = 16; body mass index [BMI], 22 to 26 kg/m2), moderately obese (n = 15; BMI, 27 to 30 kg/m2), and obese (n = 15; BMI, 31 to 37 kg/m2) men underwent a 9-month endurance exercise training program. The groups differed in the initial degree of obesity, waist circumference, and waist to hip ratio (WHR), but not in age or maximal aerobic capacity ( VO2max). The obese group had lower baseline levels of high-density lipoprotein cholesterol (HDL-C) and HDL2-C, and higher triglyceride (TG) levels than the lean group. Exercise training increased VO2max to a comparable degree in lean, moderately obese, and obese groups (18%, 24%, and 18%, respectively, P < .01). Exercise training significantly decreased TG levels in all groups, whereas total cholesterol and low-density lipoprotein cholesterol (LDL-C) decreased only in the obese group. Exercise training increased HDL-C and HDL2-C levels in lean (14% and 81%, respectively, P < .05) and moderately obese (7% and 59%, respectively, P < .05) men, whereas neither HDL-C nor HDL2-C changed in obese men. The change in HDL-C correlated negatively with initial BMI (r = -.42, P < .01) and waist circumference (r = -.43, P < .01). These results show that the effects of exercise training on HDL-C are blunted in obese middle-aged and older men, whereas improvements in TG occur independently of the degree of obesity.