In the present study, it was found that the susceptible variety Khao-tah-haeng 17, at all four predisposing temperature regimes, produced more typical lesions than hypersensitive lesions when inoculated with most of the blast fungus isolates. Tetep, Carreon, IR36 and Sensho produced more hypersensitive lesions than typical lesions at all four predisposing temperature regimes. Highly significant differences among predisposing temperature regimes and rice varieties for number of hypersensitive lesions and number of typical lesions were found. Symptom occurrence on a specific variety, as measured by the number of typical lesions, was more affected by predisposition temperature or blast isolate than by temperature and isolate combined. Symptom occurrence on a specific variety, as measured by the number of hypersensitive lesions, was more affected by blast isolate than by predisposition temperature.