Isometric exercise causes a substantial rise in BP in normotensive and untreated hypertensives. The authors studied the isometric hand-grip test in 5 groups of treated hypertensives, namely beta-blockers, beta-blockers + diuretics, beta-blockers + diuretics + vasodilators, alpha-methyldopa alone and labetalol. All groups showed a substantial rise in both systolic and diastolic BP, and the increments in BP differed little from that in normotensives. Some patients, despite multiple therapy, achieved increments of up to 60 mmHg from rest. Treated hypertensives with cardiac and cerebro-vascular disease are at risk performance isometric exercise.