The change of peroxidase and phenylalanine ammonia lyase activities was investigated on susceptible potato leaves inoculated with Phytophthora infestans after treating with exogenous DNA fraction from resistant interspecific hybrid. The increase of peroxidase activity of the leaves inoculated with Phytophthora infestans after treating with the DNA faction from the resistant hybrid was similar to that of the resistant interspecific hybrid inoculated with the incompatible race of Phytophthora infestans. Pattern of phenylalanine ammonia lyase activity in susceptible cultivar inoculated with Phytophthora infestans aLter treating with exogenous DNA fraction from resistant hybrid was similar to that of resistant hybrid inoculated with an incompatible race of Phytophthora infestans.