Ten normal subjects performed a 90-s isometric exercise [20, 30, and 40% of maximal voluntary contraction (MVC)] of the flexor muscle of the right index finger or quadriceps muscle of the right leg. Contralateral forearm and calf blood flows (strain gauge plethysmography) and arterial blood pressure (auscultation) were measured simultaneously. Each exercise caused a decrease in forearm vascular resistance and a progressive increase in calf resistance. These changes were greatest with the 40% MVC. With finger exercise at 20 and 40% MVC, the percentage decreases in forearm vascular resistance from control were 12.3 and 22.7%, respectively (P < 0.01). Similar decreases (9.5 and 24.9%, respectively; P < 0.01) were noted with exercise of the quadriceps muscle. By contrast, the corresponding increases in calf vascular resistance were greater (P < 0.01) with quadriceps exercise (13.3 and 55.4%, respectively) than with finger exercise (6.0 and 36.0%). Arrest of the circulation to the exercising muscles just before the exercise ended caused an abrupt increase in forearm vascular resistance and a decrease in calf resistance. These studies provide further evidence of the heterogeneity of responses of forearm and calf resistance vessels to certain cardiovascular stimuli.