PCR amplification of the internal transcribed spacer regions and 5.8S gene of rDNA and sequencing or restriction digestion of the resultant product were used to confirm the identities of a collection of Phytophthora isolates from a variety of hosts in Italy. All isolates were of previously described species, but a number of new host-pathogen combinations of potential economic importance were found, including P. palmivora on olive (Olea europaea) trees. Three Phytophthora isolates from chestnut (Castanea sativa) trees were identified as P. cambivora, a known pathogen of chestnut. Existing, but previously unpublished, rapid, sensitive, DNA-based assays for P. cambivora and P. cinnamomi are described. In combination with similar diagnostics for other species such as P. cactorum, these assays could be used to detect nearly all important Phytophthora species known to occur in chestnut.