Ultrastructure of young shoots and leaves of potatoes (Irish Cobbler and Norin No. 1 --compatible to Phytophthora infestans Race 0 and Interspecific hybrid 1506-(b)9 and 96-56-- incompatible to Race 0) inoculated with P. infestans was observed under electron microscope. Crystal-containing microbodies with single membrane were observed in potato cells. They were recognized in both resistant and susceptible varieties on the healthy control and inoculated plots, but sometimes crystal-containing microbodies were abundant in cells of resistant interspecific hybrid 1506-(b)9 infected with Phytophthora infestans Race 0. Microbodies were observed frequently near endoplasmic reticulum in the potato cytoplasm.