Leaves of bamboo(Phyllostachys bambusoides Sieb. et Zucc.) grown in the fields were injection-inoculated with the following 7 isotates of Pyricularia oryzae(rice isolates）and 6 isolates of Pyricularia sp. from bamboo(bamboo isolates). Rice isolates：Ken 53-33, Ken 54-04, Ken 60-19, P2b, Naga 87, Hoku 1, TY 70-94. Bamboo isolates: T300, T400 T401, T 402, T403, T609. In general, small brown spots with tiny necrotic gray centers developed on the bamboo leaves inoculated with rice isolates. Of the 7 rice isolates tested, 6 produced conidia on the lesions of the bamboo leaves when moistend. Isolates P2b and Naga 87 produced more conidia than the other. On the other hand, large spindle-shaped brown lesions with necrotic gray centers developed on the bamboo leaves inoculated with all bamboo isolates except isolate T300. Much sporulation also occurred on the lesions of the bamboo leaves in nature. The above-mentioned 7 rice isolates, and isolate Ina 72, and 4 bamboo isoiates were inoculated to bamboo(Semiarundinaria viridis Makino) by using the sheath inoculation method. The penetration rate was shown as the percentage of appres soria producing infection hyphae. The average value for the 8 rice isolates was as low as 17.9%. The value for isolate P2b was highest (35.4%), followed by isolate Naga 87 (30.9%). On the contrary, the average value for the 3 bamboo isolates, except isolate T300, was as high as 69.7% (isolate T609, 83.8%; isolate T400, 68.6%; isolate T403, 56.7%). The value for isolate T300 was as low as 18.1%.