A mechanically transmissible virus obtained from symptomless plants of a red raspberry selection imported into Scotland from Quebec, Canada was indistinguishable serologically from a cherry isolate of CRLV. The raspberry isolate, CRLV-R, was graft transmitted to several virus indicator spp. and cultivars of Rubus without inducing noticeable symptoms. In Chenopodium quinoa sap, CRLV-R lost infectivity after dilution to 10-5 or heating for 10 min at 60C but was infective after 16 d (the longest period tested) at 18C, 4C or -15C. The virus particles are isometric, c. 28 nm diam., and were purified with difficulty from infected C. murale and C. quinoa plants. The particles comprise 2 nucleoprotein components with sedimentation coefficients of 89 and 115S and are prone to aggregate during purification. When centrifuged to equilibrium in Cs2SO4 solution, purified virus preparations formed 2 major components with ρ=1.28 and 1.36 g/cm?. Virus particles contained 2 RNA species which, when denatured in glyoxal and electrophoresed in agarose gels, had estimated mol. wt of 2.56 ? 106 (RNA-1) and 1.26 ? 106 (RNA-2). Infectivity of CRLV-R RNA was abolished by treatment with proteinase K, suggesting that the RNA is linked to protein necessary for infectivity; RNA molecules contained polyadenylate. In reticulocyte lysates, CRLV-R RNA stimulated the incorporation of ?H-leucine, mainly into 2 polypeptides of estimated mol. wt 200 000 and 102 000. When electrophoresed in polyacrylamide gels, protein obtained from CRLV-R particles purified by centrifugation to equilibrium in Cs2SO4 separated into 3 bands with estimated mol. wt 26 000, 23 000 and 21 000.