Students who reported experiencing a high number of stressful life events were randomly assigned to: (a) an aerobic training condition, (b) a relaxation training condition, or (c) a no treatment control condition. Immediately before and after the 11 week training/control period, subjects' aerobic fitness and cardiovascular responses to acute psychological stress were assessed. Results indicated that: (1) subjects in the aerobic training condition showed significantly greater improvements in aerobic fitness than subjects in the other conditions, and (2) the subjects in the aerobic training condition showed significantly greater reductions in heart rate during all phases of the stress than subjects in the other conditions. Post-training differences between aerobic and control conditions during the moderate psychological stress were as great as 17 b.p.m. These results provide evidence for the utility of aerobic training for reducing cardiovascular activity during psychological stress, and they are consistent with earlier findings linking fitness to less illness following stress, reductions in depression and enhanced recovery in cardiac patients.