Chicken gizzard smooth muscle is unusual as it contains an impressive amount of the respiratory pigment myoglobin, comparable to concentrations found in the skeletal muscle of marine vertebrates. This high concentration seems to be related to the metabolism of this particular smooth muscle. Like heart muscle, where no evidence of any glycolysis in the normally beating heart in situ was found (Bing and Michal, 1958), gizzard smooth muscle appears to function almost entirely aerobically, lacking glycogen and free glucose (Gröschel-Stewart and Zuber, 1990) and showing high levels of enzymes of the oxidative pathway (unpublished results). As the blood supply of the gizzard muscle is not as extensive as that of the heart, high levels of myoglobin are needed in gizzard to supply sufficient oxygen for its forceful and lasting contractions. In addition to its function as a respiratory pigment, myoglobin of bovine (Moore ef a/., 1993) and rat skeletal muscle (Gloster and Harris, 1977) was shown to bind fatty acids, although these results were debated by others (Glatz and Veerkamp, 1983, Said and Schulz, 1984).