An aphid-transmitted virus code-named 52V is widespread in red raspberry, from which it is transmissible with difficulty by inoculation of sap to Chenopodium quinoa. Its dilution end-point in C. quinoa sap is only 10-1-10-2; partially purified preparations obtained by ether clarification and differential centrifugation contained much phytoferritin and a few isometric virus-like particles c. 2530 nm in diameter. Attempts to produce an antiserum using virus purified by sucrose density gradient centrifugation were unsuccessful. Although 52V has not been returned from C. quinoa to raspberry it was present in plants that indexed positively for black raspberry necrosis virus but were free from all other known viruses. When leaf tissue from such plants and from 52V-infected C. quinoa was examined by electron microscopy, spherical particles (c. 2025 nm) were found in the plasmodesmata. Present evidence suggests that 52V is equivalent to black raspberry necrosis virus.