Apparent varietal resistance toPhytophthora infestans among tubers of potato varieties differed when the tubers were inoculated through eyes, wounds of different sizes, or on freshly cut surfaces. Invasion by the fungus increased with greater concentrations of inoculum. Tubers of certain R1 varieties were infected relatively easily by race 0, especially through wounds; others were infected only rarely. R1 varieties differed in non-hypersensitive resistance when inoculated with race 1. Varieties also differed in relative tuber and foliage resistance