Scions from red raspberry (R. idaeus) plants naturally infected with an aphid- and sap-transmissible virus, code named 52V, always induced apical necrosis in R. occidentalis, signifying the presence of black raspberry necrosis virus whereas plants free from 52V did not. These and other findings provide strong circumstantial evidence that 52V is an isolate of BRNV, the heat-labile member of the pair of viruses that together cause raspberry veinbanding mosaic disease. On grafting with R. idaeus scions containing a 52V culture of BRNV free from other detectable viruses, all of 22 red raspberry cvs. And 4 other Rubus. spp. were infected symptomlessly but apical necrosis developed in R. henryi and R. molaccanus. Electron microscopy of thin sections of 52V-infected Chenopodium quinoa, R. henryii and R. occidentalis showed areas of dead cells in the vascular tissue and leaf blade. Some of the cells adjacent to these areas had cell wall outgrowths and many of the plasmodesmata contained virus-like particles c. 25 nm diam., arranged in a single file.