The pathogenesis-related protein, chitinase, is implicated in the resistance mechanisms involved in dogwood anthracnose, which is caused by Discula destructiva. Chitinase isozymes were isolated from Discula-inoculated Cornus mas, a highly resistant species, and from inoculated C. florida, a highly susceptible species. Chitinase activity was identified in C. mas on days 2-12 following inoculation, but was expressed only on day 8 following inoculation in C. florida. Both dogwood species expressed a constitutive chitinase level in noninoculated control leaves, but Discula-inoculated leaves of C. mas contained three chitinase isozymes, whereas C. florida leaves expressed only two. Molecular masses of isozymes were 21, 32, and 35 kDa for C. mas and 21 and 35 kDa for C. florida. Isoelectric focusing demonstrated three chitinase isozyme isoelectric points for C. mas (pI = 5.6, 6.8, and 8.9), but only two for C. florida (pI = 5.6 and 6.8). These differences in synthesized isozymes and rate of accumulation suggest that chitinase may have a role in the defense of dogwood against D. destructiva infection.