Introduction A primary polymyopathy accompanied by myocardial necrosis has been described in an inbred line (BIO 1.50 Whitney) of Mesocricetus auratus.1 This report deals with preliminary studies which indicate that this disease, or the susceptibility thereto, probably is genetically controlled. The Disease.— Clinical Observations: This disease occurs in all animals of the BIO 1.50 (Whitney) strain, which has been derived from a white LaCasse sire and a brown Schwentker dam and has been carried through 19 generations of brother/sister mating. The onset is gradual, and the first symptoms of weakness and difficulty in motion and coordination appear at about 180 days (60-220 days) of age. Occasionally, in malnourished animals, the onset may be earlier. Once the animals show signs of muscular weakness, many of them also begin to have edema of dependent parts of the body, and finally they died on the average at 220 days of age, which