Seven red raspberry cultivars reacted differently to infection at 2 commercial plantations in Scotland and North Wales. Latham, Chief and Boyne were completely resistant. Malling Delight and Glen Clova supported more telial sori than Malling Jewel. In contrast Malling Jewel was the most susceptible cultivar at the aecial stage in Scotland but developed similar numbers of aecia to Glen Clova and Malling Delight in Wales. Meeker had an extended latent period, fewer and smaller pustules and a very small yield of urediospores compared with the other susceptible cultivars, thus showing the characteristics of slow-rusting genotypes. At the Scottish site in 1982, where rust was less than in Wales, Meeker and Malling Jewel performed differently from the other cultivars at the telial stage. Inoculation studies under controlled environmental conditions with urediospores from each site revealed an interaction between cultivars and isolates, suggesting variation in pathogenicity in populations of P. rubi-idaei in the United Kingdom.