An attempt was made to assess the effects of aerobic exercise on the psychological functioning of a nonclinical sample of healthy middle-aged adults. Sixteen subjects participated in a 10-week program of regular walking-jogging, while a matched control group maintained their sedentary life-styles. All subjects completed a battery of psychological tests, including the Profile of Mood States, the State-Trait Anxiety Inventory and a retrospective questionnaire regarding self-perceptions of change. Examination of test scores revealed that scores for the exercise group almost always improved, whereas the scores for the control group remained the same or deteriorated. The exercisers exhibited less state and trait anxiety, less tension, depression, and fatigue, and more vigor than the controls. These results document the potential utility of regular aerobic exercise in promoting psychological health in normal adults.