In 13 subjects intra-arterial blood pressure, heart rate, blood lactate, oxygen consumption, and pulmonary ventilation were respectively measured during submaximal and maximal arm and leg exercise. Blood pressure usually increased linearly with the oxygen uptake, this increase being significantly more pronounced for arm than leg work. The site of the catheter, mostly the femoral artery, can partly account for the difference, recorded blood pressure being constantly higher in the resting limb. Nevertheless, simultaneously recorded pressures in arm and leg give significantly higher values during cranking. Larger increases in peripheral vascular resistance in the resting extremities during arm work as well as the important static work produced by cranking are possible explanations for this difference. This fact might have clinical interest. differences between arm and leg work; catheter position when measuring blood pressures; lactate production in small and large muscle groups Submitted on June 15, 1964