In accordance with its lack of inhibitory activity against pig pancreatic kallikrein, Tos-LysCH2C1 has been shown also not to inhibit the porcine kallikreins from submandibular glands and from urine. Peptidyl-lysyl-chloromethanes, however, have been demonstrated to be irreversible inhibitors of all three enzymes. The rates of inhibition increase with increasing size of the amino acid residue in position P2 of the inhibitors. As expected from the known primary specificity of the pancreatic kallikrein, Gly-Val-ArgCH2C1 was found to be the most potent of the inhibitors studies. Kinetic constants for the inhibiton of the three porcine glandular kallikreins have been determined for two of the compounds. All data obtained suggest a close similarity of the three glandular kallikreins of the pig and even a possible identity of the enzymes from submandibular glands and from urine.