<p>From the histochemical study on the vascular distribution of limb muscles of cats and rats, the following results were obtained. 1. The red, white and intermediate fibers of the soleus and gastrocnemius individually present dissimilar patterns of the vascular distribution. In the transverse section of the muscle, most of the capillaries are found preferentially assembled around the small red fiber. Usually the red fibers are supplied with 4-6 capillaries, while the intermediate fibers 3-4 capillaries and the white 1-2 capillaries. 2. In the longitudinal section, the capillaries run parallel with the muscle fiber. Occasionally, these capillaries branching out for anastomoses cross the fiber almost at right angle. These anastomoses are more frequently observed on the red fibers. 3. The soleus muscle is better supplied with capillaries than is the gastrocnemius, because this muscle is composed only of two types of capillary rich fibers, namely, the red and intermediate fibers. 4. The mean capillary-fiber ratio of the cat gastrocnemius proves to be 0.6 and that of the soleus 1.4. 5. From these observations, it is considered that there is an intimate relationship between the capillary distribution pattern and the type of individual muscle fibers. 6. The red fibers being with a high oxidative enzyme activity and rich in mitochondria may require an abundant supply of oxygen and have a greater number of capillaries. In contrast to this, the white fibers with a lower enzyme activity and a fewer mitochondria need not to consume so much oxygen and are supplied with a fewer capillaries, because they participate only in phasic contraction. The intermediate fibers, with a moderate enzyme activity, may be considered to have a moderate number of capillaries.</p>