Summary: Peroxidases participate in many reactions and regulate multiple processes in the plant. Among these, chitin-binding peroxidases play a key role. We have investigated peroxidase activity in seven Upland cotton cultivars, and we found that a two-fold increase occurred in the resistant cotton variety AN-BAYAUT – 2 after inoculation with Verticillium dahliae. The peroxidase activity in the resistant variety was due to biosynthesis of chitin binding peroxidase isozymes. The susceptible cotton line C-4727 also showed an increase in peroxidase activity, but most of these peroxidase isozymes did not bind to chitin.