An improved method for isolating intact lysosomes from beef muscle is presented, using an unspeciüc bacterial protease (nagarse, 50 lg ml-1) prior to homogenisation. Nagarse treatment resulted in 100% increased cathepsin B + L activities in the membrane fraction (subcellular fraction containing lysosomes). By using this method the subcellular distribution of lysosomal enzymes, as aþ ected by parameters related to meat marination, was investigated in beef muscle. Diþ erent prerigor lactic acid treatments were performed in a muscle homogenate, in a muscle mince ünely cut with scissors, and in whole muscle. The eþ ect of lower pH on the level of free (not bound) enzyme activities was dependent on muscle integrity. Lowering pH in the muscle homogenate from 7.2 to 5.0 shifted the majority of cathepsin B + L and b-glucuronidase activities from the membrane fraction into the myoübrillar fraction. In contrast, decreased pH of the muscle mince increased enzyme activities in the soluble fraction (P AE 0.05). Also the lactic acid injection procedure resulted in increased activities of lysosomal enzymes in the soluble fraction (P AE 0.01). Storage for up to 4 days resulted in a gradual increase in free enzyme activity also in control samples, but to a lower ünal level as compared to lactic acid treated samples.