Purified preparations of an isolate of BRLV contained quasispherical particles with a mean diam. of 28.5 nm; these particles were resolved into 3 sedimenting components (s20,w = 82S, 95S and 104S) but when centrifuged to equilibrium in caesium chloride solution they formed a single infective band ( rho = 1.35 g/cm3). During electrophoresis in polyacrylamide gels, virus particles separated into 3 classes, and virus RNA was resolved into 3 major (mol. wt. 1.35, 1.1 and 0.85 X 106) and 1 minor (mol. wt. 0.4 X 106) component. The protein from virus particles had an estimated mol. wt. of 28 000. Isolates of BRLV were found to be serologically related but not identical with some strs. of TSV. No symptoms developed in black raspberry seedlings infected with BRLV by mechanical inoculation, or in 8 red raspberry cvs. infected by graft inoculation. However, graft inoculation of BRLV to Rubus henryi, R. phoenicolasius and Himalaya blackberry induced symptoms typical of necrotic shock disease.