To clarify the relationship between histological events and lesion formation in incompatible rice and rice blast fungus interaction, penetration frequency, growth of infection hyphae, and cellular reactions were compared in 12 cultivars, each of which showed one of the following four resistant reactions: highly resistant, resistant, moderately resistant, or intermediate. Penetration frequency varied depending on the cultivar, leaf age, and fungal isolate. Papilla-like structures were observed at some unsuccessful penetration sites, but their formation was too restricted to be responsible for the penetration failure of most conidia. Growth of infection hyphae stopped before 24 h in highly resistant cultivars, before 36 h in resistant cultivars, and later than 36 h in moderately resistant cultivars. The growth inhibition of infection hyphae was coincident with the occurrence of a light brown coloration and aniline blue staining of cell walls (B reactions) around infection sites in these cultivars. These results indicate a close relationship between occurrence of B reactions and growth inhibition of infection hyphae and suggest that the time required for B reactions to occur and for growth infection hyphae to stop varies according to degree of host resistance.