Exercise induced plasma catecholamine levels, of post myocardial infarct patients, were compared before and after a 27 wk training program in 2 groups, heavy intensity exercise (H.I.E.) and light intensity exercise (L.I.E.). The men (age 38-54 yr) were exercised on a bicycle ergometer at constant submaximal work loads (test load) and to a symptom limited maximum work load, both before and after the training program. Forearm venous samples were obtained after 30 min rest and within 3 min of completion of the test load. After training a significant increase in both maximum work load and heart rate (P < 0.05) was observed in the H.I.E. group. At the test load these individuals had a small (6%) decrease in heart rate. No significant changes were observed in the L.I.E. group at submaximum or maximum exercise. Prior to training, exercise resulted in a significant increase in norepinephrine (NE) with no change in epinephrine (E). Training resulted in a significant reduction (P < 0.05) in the NE response at the test load of the H.I.E. group while no change was found in the L.I.E. group. Endurance jogging reduced the sympathetic response to moderate exercise.