SUMMARYPurified preparations of an isolate of black raspberry latent virus (BRLV) contained quasispherical particles with a mean diameter of 28·5 nm; these particles were resolved into three sedimenting components (s20, w= 82S, 95Sand 104S), but when centrifuged to equilibrium in caesium chloride solution they formed a single infective band (σ= 1·35 g/cm3). During electrophoresis in polyacrylamide gels, virus particles separated into three classes, and virus RNA was resolved into three major (mol. wt 1·35, 1·10 and 0·85 × 106) and one minor (mol. wt 0·4 × 106) component. The protein from virus particles had an estimated mol. wt of 28000. Isolates of BRLV were found to be serologically related but not identical to some strains of tobacco streak virus.No symptoms developed in black raspberry seedlings infected with BRLV by mechanical inoculation, nor in eight red raspberry cultivars infected by graft inoculation. However, graft inoculation of BRLV toRubus henryi, R. phoenicolasiusand Himalaya blackberry induced symptoms typical of necrotic shock