Rice leaf sheaths were inoculated with R. solani (pathogen) and P. palmarum (non-pathogen) and were analyzed for the accumulation of pathogenesis-related (PR) proteins. Inoculation of rice plants with R. solani and P. palmarum resulted in a marked increase in activities of chitinase and b-1,3-glucanase. The levels of both enzymes were higher in incompatible interactions than in compatible interactions. Western blot analysis indicated that two proteins with molecular weights of 33 and 35 kDa cross-reacting with barley chitinase antibody were induced in rice in response to inoculation with R. solani. The appearance of these chitinases was correlated with increase in enzyme activity.