The extent and duration of serum lipid and lipoprotein changes were examined in 12 mildly obese women who walked 45 minutes at 60% VO2max in a laboratory setting. A two-factor, 2 x 6 design with repeated measures on both factors was utilized. The first factor was condition (exercise and rest) and the second factor was time (six times of measurement over a 24-hour period) with treatment counterbalanced. The patterns of change in total high-density lipoprotein-cholesterol (HDL-C) [F(5,55) = 5.75, p less than 0.001] and HDL3-C [F(5,55) = 2.62, p = 0.034], but not HDL2-C [F(5,55) = 1.15, p = 0.346], were significantly different between conditions. Relative to baseline and the rest condition, total HDL-C tended to rise due to a significant 11.6% increase in HDL3-C immediately post-exercise, with values returning to baseline 1.5 hours post-exercise. The interaction statistic for triglycerides was significant with trends for a decrease in triglycerides at 1.5 and 23 hours post-exercise relative to baseline and the rest condition. No significant differences were seen between the exercise and rest conditions for total cholesterol, low-density lipoprotein cholesterol, glucose, or plasma volume. These data indicate that an exercise intensity achievable by brisk walking (7.4 kph) is sufficient to evoke significant but short-term changes in serum HDL3-C concentrations in women.