DNA from P. fragariae var. rubi was cloned in E.coli, and clones showing little or no hybridization to other Phytophthora species in dot blots were selected for use as probes which might detect restriction fragment-length polymorphisms (RFLPs) within and between the proposed varieties P. f. var. rubi and P. f. var. fragariae. Variation revealed by restriction enzyme digestion of mtDNA was also employed. Both pathogens were very homogenous, providing support for their recent and rapid worldwide expansion. Although readily distinguishable, they were more closely related to one another than to any other Phytophthora species, and it is suggested that their separation at the variety level is appropriate. Two of the probes also proved suitable for differentiating among other Phytophthora spp. associated with raspberry root rot.