The purpose of this study was to characterize the short-term changes in blood lipid and apolipoprotein concentrations in healthy hypercholesterolemic men after high-intensity [80% maximal O2 uptake (VO2max); n = 20] or moderate-intensity (50% VO2max; n = 19) cycle ergometer exercise balanced for caloric expenditure (350 kcal). The men's age, height, weight, %fat, and VO2max were 46 +/- 2 yr, 173 +/- 7 cm, 82.7 +/- 2.2 kg, 28 +/- 1%, and 31.1 +/- 1.0 ml O2.kg-1.min-1, respectively. Blood samples were drawn before exercise, immediately after exercise, then 24 and 48 h later, and concentrations of all variables were adjusted for changes in plasma volume. Significant changes (P < 0.0016) were as follows: total and low-density lipoprotein cholesterol fell by 4% immediately after exercise and then rose by 5-8% by 48 h. Triglycerides were 18 and 15% lower at 24 and 48 h, respectively. HDL-cholesterol, high-density lipoprotein3-cholesterol, and apolipoprotein B rose 8-9% by 24 h and remained elevated. High-density lipoprotein2-cholesterol rose by 27% by 48 h after exercise, but this change was not significant. Apolipoprotein A-I did not change with exercise. The response patterns were not affected by exercise intensity. These data show that a single session of exercise performed by untrained hypercholesterolemic men alters blood lipid and apolipoprotein concentrations. Furthermore, the postexercise response patterns are not influenced by exercise intensity, as long as caloric expenditure is held constant.