Phytophthora capsici and P.parasitica were transformed to hygromycin B resistance using plasmids pCM54 and pHL1, which contain the bacterial hygromycin B phosphotransferase gene (hph) fused to promoter elements of the Ustilago maydis heat shock hsp70 gene. Enzymes Driselase and Novozyme 234 were used to generate protoplasts which were then transformed following exposure to plasmid DNA and polyethylene glycol 6000. Transformation frequencies of over 500 transformants per μg of DNA per 1 × 106 protoplasts were obtained. Plasmid pCM54 appears to be transmitted in Phytophthora spp. as an extrachromosomal element through replication, as shown by Southern blot hybridization and by the loss of plasmid methylation. in addition, transformed strains retained their capacity of infecting Serrano pepper seedlings and Mc. Intosh apple fruits, the host plants for P.capsici and P.parasitica, respectively.