When rice leaf-sheaths were infiltrated with the homogenates from healthy rice leaves and then inoculated with the incompatible race of Pyricularra oryzae, remarkable hyphal growth in the tissues was observed. The homogenates increased hyphal growth indices of the incompatible races, regardless of whether the rice cultivars used to prepare the homogenates were resistant or susceptible to the races of the rice blast fungi inoculated after the homogenate treatment. Such an induced-susceptibility was also recognized in the rice leaf-sheaths pre-treated with the boiled(100 C-30 min)-homogrenates. In case of post-inoculation with Pyricularia sp., non-pathogenic to rice plants, the hyphal growth in the leaf sheaths pre-treated with leaf homogenates was nearly the same values as that of pretreatment with distilled water, and the values of both the average and highest indices were also found to be very poor.