Excessive meat tenderization in cured raw Parma ham has recently been correlated with abnormal levels of cathepsin B in freshly slaughtered thigh meat. We have developed a visual assay employing the substrate Z-Arg-Arg-NNapOMe for the quantitative detection of active cathepsin B levels in pork thigh muscle homogenates. The work was based on a kinetic characterization, in steady state condition, of pig muscle cathepsin B with several peptidyl chromophoric substrate analogs. This assay can easily and safely be performed by non-specialized personnel directly in the slaughterhouse or in the factory, for an early quality evaluation of thighs selected for Parma ham production. Our characterization has further indicated that the catalytic properties of porcine muscle cathepsin B and those of isoforms from other animal and plant species are practically identical. This is particularly evident in the commercially available bovine spleen isoform, which was employed as a model enzyme in most of the experiments.