Randomized, controlled trial. Known hypertensives (n=162) whose diastolic blood pressures rose to between 90 and 104 within four months of discontinuing medication under careful observation had their pressures controlled with enalapril. Oxygen consumption (V02) peak was measured during cycle ergometry. Eligible subjects were randomly assigned to 18 months participation in one of three groups: 1) high intensity endurance training (35 minutes three times/week at heart rate at 70-85 percent of V02 peak), 2) moderate intensity endurance training (35 minutes three times/week at heart rate of 50-70 of V02 peak), and 3) contact control. Enalapril was forward or back titrated or discontinued to maintain a normal blood pressure. After 12 months participation, medication was withdrawn under careful supervision from all subjects still taking it. The trial tested the hypotheses that: 1) a greater number of subjects undergoing either or both of the two 18 month exercise training programs would be able to stop anti-hypertensive medication than non-exercising controls, 2) moderate and high intensity endurance training were equally effective in replacing drugs in the treatment of mild essential hypertension, and 3) subjects that were successful at withdrawing anti-hypertensive medication would have: greater improvements in V02 peak, better initial psychological status or greater improvements in psychological status, and greater compliance with the exercise training program.