SUMMARY—Experiments were conducted to determine the effect of post‐mortem temperatures between 0 and 20°C on the degree of shortening in isolated pectoralis major muscles of chickens and turkeys. A “cold shortening” effect in these muscles is described and compared to post‐mortem pH, average sarcomere length of isolated myofibrils, and relative solubility of myofibrillar and sarcoplasmic proteins.The degree of muscle shortening at each temperature after various periods post‐mortem indicated that shortening was essentially complete after 3 hr in chickens and 5 hr in turkeys. Shortening in muscles stored at 0°C was significantly greater (P.05) with shortening. Extractability of myofibrillar and sarcoplasmic proteins after 5 hr at either 0 or 16°C was determined and found to be unrelated to the degree of po