In leaves of the susceptible host, weeping lovegrass, strain 4091-5-8 of the rice blast fungus, Magnaporthe grisea, elicited no ultrastructurally detectable responses of underlying epidermal cells during appressorium development or penetration peg formation. During the subsequent growth of the fungus both inter- and intra-cellularly, leaf cells initially showed little obvious response even after fungal penetration, although the cytoplasm of invaded cells eventually became disorganized. In leaves of the less susceptible goosegrass, successful penetration from appressoria was rare and usually resulted in rapid death of both fungus and epidermal cell. Most frequently, however, fungal growth ceased at various stages during the formation of the penetration peg, in association with the deposition of highly electron-opaque material in the underlying epidermal wall. From their ultrastructural appearance, and their natural electron opacity after osmium removal with periodate, these deposits appeared to contain silica. Key words: rice blast, wall appositions, silica.