Although exercise training has been demonstrated to improve lipid profiles in young and middle-aged subjects, the response in training in the elderly has received little attention. In this study, we assessed and compared the changes in aerobic capacity, lipid profiles, and body composition in young (Y, 31.9 +/- 5.5 years; n = 18) and older (O, 65.1 +/- 6.1 years; n = 10) subjects in response to similar 3-month exercise training programs (80% to 85% of heart rate reserve, three times per week). We hypothesized that the responses would be qualitatively similar for the two groups, although the absolute quantitative response might be somewhat less in the elderly. The two groups were quite similar at baseline for percent body fat (Y, 30.1% +/- 7.2% v O, 30.3% +/- 4.7%; P = NS) and maximal aerobic capacity (Y, 36.8 +/- 8.1 v O, 36.3 +/- 8.3 mL/kg/min; P = NS). In addition, there were no significant differences in the baseline lipid profiles between the groups. After training, the improvements in body composition were similar, with both groups losing similar amounts of fat (Y, 2.86% +/- 3.14% v O, -2.85% +/- 1.78%) and neither group significantly changing their fat-free mass. Maximal aerobic capacity improved in both groups, but the increment was greater in the young (18% v 10%, P less than .05). HDL-cholesterol (+6%, P less than .01) and apolipoprotein A-I (+6%, P less than .01) concentrations increased significantly only in the young. These increments, however, were not different from those observed in the older subjects (+7% and +4%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)