The prevalence of systemic hypertension and its cardiovascular consequences is higher in African-Americans than in whites. Low to moderate intensity aerobic exercise lowers blood pressure (BP) in African-American patients with severe hypertension. It is not known whether such exercise can improve lipid metabolism in these patients. Thirty-six African-American men with established essential hypertension, aged 35 to 76 years, were randomly assigned to an exercise (n = 17) or no exercise (n = 19) group. The exercise group exercised for 16 weeks, 3 times/week, at 60% to 80% of maximum heart rate. After 16 weeks, peak oxygen uptake in the exercise group improved (21+/-4 vs 23+/-3 ml/kg/min; p <0.001). Body weight did not change. Exercise intensity correlated with high-density lipoprotein (HDL) cholesterol changes from baseline to 16 weeks (r = 0.65; p <0.01) and was the strongest predictor of these changes (R2 = 0.4; p = 0.009). Lipoprotein-lipid changes in the 2 randomized groups did not differ significantly. A 10% increase in HDL cholesterol--42+/-19 versus 46+/-19 mg/dl; p = 0.003--noted in 10 patients who exercised > or = 75% of maximal heart rate suggested the existence of an exercise intensity threshold. Thus low to moderate intensity aerobic exercise may not be adequate to modify lipid profiles favorably in patients with severe hypertension. However, substantial changes in HDL cholesterol were noted in patients exercising at intensities > or = 75% of age-predicted maximum heart rate, suggesting an exercise-intensity threshold.