Muscle blood flow in the anterior tibial and gastrocnemius muscles of 40 limbs with thromboangitis obliterans with occlusions only in the leg arteries was measured by Xe-133 non-ischemic work method. All cases with complete occlusion at the origin of the anterior tibial artery had remarkably abnormal curves in the anterior tibial muscle. All cases, except one, with occlusion of the posterior tibial artery at its origin or at the origin of the peroneal artery had moderate abnormal clearance curves in the gastrocnemius muscle. Even if the peroneal artery was completely occluded the clearance curve in the gastrocnemius muscle was normal. In producing intermittent claudication in the calf without occlusion proximally to the popliteal artery, the sural arteries, the posterior tibial artery and the muscle nutritive arteries are very important.