Thirty-seven immature nematodes of the genus Physaloptera were found embedded in the breast and thigh musculature of an adult male Richardson's grouse (Dendragapus obscurus richardsonii, Douglas), collected in the Highwood district of southwestern Alberta on September 9, 1958. Each white larval nematode (Fig. 1) measured approximately 4 mm. long and 0.3 mm. in diameter, and was found curled in an orange-colored fluid within a flat-topped transparent cyst approximately 5 mm. in diameter. Examination of the other organs and intestinal contents of this and three other Richardson's grouse collected at the same time, failed to reveal any other tissue pathology, parasites or parasite ova. Hegner, et al. (1938) group the Physaloptera in the sub-family Physalopterinae, family Spiruridae, order Filarioidea, indicating that they are parasites of the digestive tract, generally the stomach of reptiles, birds and mammals. They mention that the life history of this group generally is unknown, but probably involves intermediate stages in insects or other hosts. Chandler (1950) reports that nematodes of this genus most frequently live in the stomach, intestine and occasionally the liver, burying their heads in the mucous membrane and causing sores and ulcerations. Wehr (1958) writes, "Immature forms of these nematodes and related genera have frequently been found encysted within the body cavities of birds and mammals, however, we know of no previous record of any of these larval forms being collected from the breast and leg muscles of a bird." Bendall (1955) studying 103 specimens of the sooty blue grouse (Dendragapus obscurus fuliginosus, Ridgway) from Vancouver Island, B.C., and Boag (1958), examining 74 Richardson's grouse from the Sheep District in Alberta, did not find this parasite. As far as can be determined, this is the first time that the larval form of Physaloptera sp. has been reported from the Richardson's grouse or from the musculature of an avian host.