Within the last 10 years, much attention has been focused on the role chitinases play within the plant. Evidence is strong that they are antifungal proteins, yet they may also play a part in a nonspecific stress response and can be developmentally regulated. They consist of several enzyme classes and are produced in many plants by small gene families. This review discusses the nature of these enzymes and the genes that encode them, developmental- and tissue-specific expression, and the classes of organic and inorganic molecules which induce chitinase gene expression and accumulation. Prospects for the development of fungus-resistant varieties of plants using "foreign" chitinase genes are also analyzed. Key words: pathogenesis-related protein, antifungal protein, gene regulation, induction, hydrolase.