Measures of mood, primary process, and movement were obtained from 52 subjects at each of three experimental stages: pretest, exercise, and posttest. During exercise half the subjects ran on a treadmill while the remainder served as no-exercise controls. Both groups experienced significant reductions in negative mood, but enhanced positive mood was found only for the exercising subjects. There were no significant effects of exercise on primary-process or movement scores. The experimental effects of exercise on mood and cognition are discussed in relation to anecdotal reports in the literature.