One layer of muscle homogenate rich in myoglobin (heart muscle of the rat) and three layers of muscle homogenate poor in myoglobin (skeletal muscle of the rat) were arranged one upon the other, than reseparated after a certain time. According to the concentration change of myoglobin in the layers the diffusion coefficient of myoglobin is 1.5 × 10 -7 cm2/sec at 20 ° C and 2.7 x 10 -7 cm2/see at 37 ° C. From this result it was calculated that the facilitated 02 diffusion on the basis of myoglobin diffusion amounts, at 37 ° C, to the free O 2 diffusion at about 3 mm Hg partial pressure difference when myoglobin concentration is 2 × 10 -7 tool (3 rag) per g wet muscle. Key-Words: Myoglobin -Diffusion -Muscle -Facilitated 02-Diffusion. Schli~sseIw6rter: Myog]obin -Diffusion -Muskel -erleichterte O~-Diffusion.