The purpose of this study was to determine the effect of exercise duration on lipoprotein responses. Twenty two normolipidemic male volunteers, ages 19-31 yrs (X +/- SEM = 23.1 +/- 2.94) participated in the study. Each was novice a runner (training less than 5 mi/wk). Subjects were assessed for baseline lipid measures of high density lipoprotein (HDL-C), low density lipoprotein (LDL-C), total cholesterol (TC) and triglycerides (TG). They were then evaluated for VO2max and ventilatory threshold (VT). Later they were matched for VO2max and randomly assigned to one of three groups which exercised for 15, 30 or 45 min respectively at a VO2 20% below VT. Subjects were evaluated again for HDL-C, LDL-C, TC and TG from blood samples taken pre-exercise and immediately post-exercise, as well as 1, 24 and 48 hrs post-exercise. A 3 X 4 split plot ANOVA found no difference for any lipid measure during the baseline period. A 3 X 5 split-plot ANOVA (covarying for pre-exercise measures) and post-hoc comparisons of pre- and post-exercise lipid levels indicated no significant differences occurred for either TC, TG or LDL-C measures (p less than 0.05). With respect to HDL-C, the 30 min group had significantly lower HDL-C at the 24 hr measure than did 45 min group (46.41 +/- 1.70 vs 53.34 +/- 1.73 mg.dl-1 respectively). No other differences were found. These findings indicate exercise duration will have an effect on acute responses of lipoprotein following exercise of low intensity.