The relationship between post-mortem calcium concentration in muscle and indicators of proteolysis was examined and compared with pH as a predictor of these changes. Muscle samples (m. longissimus et thoracis lumborum; LTL) were obtained from the left side of 24 lamb carcasses at pH 6.2 and 6.0 and then at 1 and 2 days post-mortem (n=96). Alternate carcasses were electrically stimulated (low voltage) within 15 min of death. The myofibrillar fragmentation index (MFI) was determined on samples taken at pH 6.2 and 1 and 2 days post-mortem (n=72). Protein solubility, pH and free calcium concentration were measured on all samples (n=96). The post-mortem degradation of myofibrillar proteins was followed using SDS electrophoresis on all samples (n=96) from which the relative amounts of the 30 kDa fragment and a protein designated M1 were quantified. Transformation of data values for each variable (MFI, protein solubility, 30 kDa fragment and protein M1) improved the normality of the residuals and increased the variance explained by either calcium concentration or pH. pH was a better predictor of MFI and the 30-kDa fragment than calcium concentration and this was reversed when protein solubility and the protein designated M1 was predicted. Of the variables protein solubility could be predicted with the greatest accuracy using calcium concentration (R(2)=0.64; R.S.D.=0.81) or pH (R(2)=0.60; R.S.D.=0.85). However overall calcium concentration was not superior to pH as a predictor of the changes in the different indicators of proteolysis examined in this study.