We tested the effect of beginning an exercise program on the mood of sedentary men who were free of psychopathology. Fourteen men were randomly assigned to either an exercise program or a control period for 12 weeks and then switched to the converse condition. The exercise was nonsocial and of moderate intensity. Exercise did not improve anger, tension, confusion, depression, fatigue, vigor, or total mood disturbance more than a control period. We conclude that beginning an exercise program, in itself, produces minimal psychological benefits. We hypothesize that other conditions, e.g. the presence of emotional problems, socialization along with exercise, or a training effect must be present for exercise to produce psychological benefits.