Eighteen patients with coronary artery disease were divided into two groups according to whether their blood pressure decreased (eight, group 1) or increased (10, group 2) in response to treadmill exercise testing. Age and the extent and distribution of coronary artery disease were similar in the two groups. At rest, blood pressure, pulmonary artery wedge pressure, cardiac index, forearm vascular resistance, and oxygen consumption were similar in the two groups. During supine leg exercise on a bicycle ergometer mean blood pressure increased in group 2 but did not change in group 1. Increases in cardiac index, pulmonary artery wedge pressure, and oxygen consumption during leg exercise were not significantly different in the two groups but forearm vascular resistance increased less in group 1 than in group 2. There was a positive correlation between the magnitude of the change in mean blood pressure and change in forearm vascular resistance during leg exercise. The impaired response of blood pressure to leg exercise in group 1 was not the result of a failure of the cardiac index to increase. The results suggest the possibility that attenuation of reflex vasoconstriction in non-exercising muscles may contribute to the impaired response of blood pressure to exercise in patients with coronary artery disease.