Fungal resistance in Euvitis is generally correlated with levels of pathogenesis-related proteins such as chitinase. Vitis rotundifolia is resistant to many pathogens that affect Vitis vinifera; therefore, grape chitinase activities were compared in V. rotundifolia cv. Fry and V. vinifera cvs. Cabernet Sauvignon and Chardonnay. Cabernet Sauvignon and Chardonnay chitinase activities were approximately 130-fold and 80-fold higher than Fry activities, respectively. Thus, the high pathogen resistance of Fry may be a result of factors other than chitinase. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fry berries had two chitinase isoforms, and at least one was not found in the V. vinifera berries. Cabernet Sauvignon and Chardonnay had four and five chitinase isoforms, respectively.