Isolates of Phytophthora fragariae var. rubi from widely separated areas of North America and Europe were inoculated in a controlled environment on to a range of red raspberry genotypes from breeding programmes in both continents. Analysis of the results showed a significant isolate/genotype interaction suggesting the existence of several races, the most common of which was found in both continents. The standard resistant genotype, Latham, was highly resistant to all isolates tested. This is the first report of races in this pathogen, although they have been recognised for many years in the closely related fungus, P. fragariae var. fragariae, from strawberry.