Studies on the correlation between expression and/or autolysis of calpain and postmortem proteolysis in muscle have provided conflicting evidence regarding the possible role of calpain 3 in postmortem tenderization of meat. Thus, the objective of this research was to test the effect of postmortem storage on proteolysis and structural changes in muscle from normal and calpain 3 knockout mice. Knockout mice (n = 6) were sacrificed along with control mice (n = 6). Hind limbs were removed and stored at 4 degrees C; muscles were dissected at 0, 1, and 3 d postmortem and subsequently analyzed individually for degradation of desmin. Pooled samples for each storage time and mouse type were analyzed for degradation of nebulin, dystrophin, vinculin, and troponin-T. In a separate experiment, hind-limb muscles from knockout (n = 4) and control mice (n = 4) were analyzed for structural changes at 0 and 7 d postmortem using light microscopy. As an index of structural changes, fiber detachment, cracked or broken fibers, and the appearance of space between sarcomeres were quantified. Cumulatively, the results of the first experiment indicated that postmortem proteolysis of muscle occurred similarly in control and in calpain 3 knockout mice. Desmin degradation did not differ (P > 0.99), and there were no indications that degradation of nebulin, dystrophin, vinculin, and troponin-T were affected by the absence of calpain 3 in postmortem muscle. Structural changes were affected by time postmortem (P < 0.05), but not by the absence of calpain 3 from the muscles. In conclusion, these results indicate that calpain 3 plays a minor role, if any, in postmortem proteolysis in muscle.