The effect of acute exercise on blood lipids and lipoproteins has been examined and their response is believed to reflect the changes that occur as a result of chronic exercise training. The cross sectional differences between trained and untrained individuals and the results of longitudinal investigations suggest LDL particle size and distribution may be altered after acute exercise. Moreover, the response of the lipid and lipoprotein profile of Black men may be different than that of White men, owing to initial concentration differences or a genetic predisposition. PURPOSE: To examine the effects of expending 300 and 600 calories through treadmill walking at a moderate intensity (65% VO2max) on blood lipids and lipoproteins as compared to a non-exercise, control trial over the course of 72 hours. METHODS: Ten White and ten Black men participated in this study after being screened for strict inclusion criteria (including: parents/grandparents either Black or White and from the United States; sedentary, but otherwise healthy; VO2max 30-45ml⋅kg⋅min-1; and body fatness ¡Ü25%). Analysis of variance with repeated measures design was used (Group x Trial x Time). Blood was collected at Baseline (0hr), 12hr, 24hr, 48hr and 72hr for determination of blood lipid concentrations, LDL particle size, LDL distribution and CETPa. RESULTS: Black men of this investigation had higher HDL-C (49.4 vs 41.8 mg⋅dL-1), HDL3-C (35.1 vs 30.8 mg⋅dL-1) and CETPa (82.1 vs 52.8 pmol⋅ml-1⋅3hr-1) and lower TC (148.9 vs 177.1 mg⋅dL- 1), LDL-C (83.4 vs 116.3 mg⋅dL-1) and TC to HDL ratios (3.06 vs 4.46) than the White men (p<0.05) over the control period. There were no group differences detected in LDL particle size (White 25.63nm vs Black 25.79nm), LDL distribution (Zone 1, White 58.19% vs Black 64.71%; Zone 2, White 20.16% vs Black 16.31%; Zone 3, White 21.65% vs Black 18.98%), HDL2-C (White 11.5 vs Black 14.2 mg⋅dL-1), or TG (White 95.0 vs Black 79.4 mg⋅dL-1). Black and White men responded to acute exercise in similar fashion for these variables and therefore our statistical model collapsed the data into a single group by trial and over time. Exercise did not statistically alter TC, LDL-C, LDL particle size, LDL distribution, HDL2-C or CETPa in the 72 hours following each exercise bout. However, HDL-C was increased 6.2%, 10.1% and 5.8%, HDL3-C was increased 9.8%, 13.8% and 9.8%, while TG were reduced 24.8%, 27.3% and 22.4% at 12hr, 24hr and 48hr, respectively from the Base value of the 600 Kcal Trial. Additionally, TG were reduced 18.0% at 12hr from the baseline value of the 300 Kcal Trial. CONCLUSION: These results are the first to indicate that acute treadmill walking at moderate intensity of sufficient caloric expenditure modified HDL-C, HDL3-C and TG in Black men. No differences were determined in the manner in which Black and White American men statistically increased HDL-C and HDL3-C and reduced TG after acute exercise. In addition, there was no impact of acute exercise on TC, LDL-C, HDL2-C, CETPa, LDL particle size or LDL distribution in either group. However, these data suggest that Black/White differences exist in CETPa, where Black men have greater activity of this enzyme.