The effects of frozen storage on the biochemical properties of myofibrils, muscle proteinases (cathepsins and calpains) and their endogenous inhibitors were investigated. Longissimus dorsi, biceps femoris, semimembranosus and semitendinosus muscles from goat were frozen (−15C) and studied up to 120 days. The results showed that the percentage change in sarcomere length was 8.4–13.1. The calpain activity was determined after separation on a diethylaminoethyl–Sephacel column (Sigma, St. Louis, MO). Significantly greater percentage of calpain II activity was recovered when compared to calpain I. There was a 15–25% loss in calpastatin inhibitory activity, and the cystatin level fell by 11–16% after 80 days. Cathepsin B, B + L, H and D were very stable when compared to calpains. The calcium concentration may also be the factor for calpain activation. The sodium dodecyl sulfate–polyacrylamide gel electrophoresis result showed the appearance of 55 kDa components. It was concluded that calpains, not cathepsins, play an important role in the proteolysis of myofibrillar proteins at the freezing temperature.