A laboratory study was carried out in the UK to determine whether particles of raspberry vein chlorosis virus occurred in tissues of the vector Aphis idaei v.d. Goot. Electron microscopy of thin sections of aphids that had fed for 14 days on plants infected with the virus revealed enveloped particles similar to those observed previously in infected plants. The particles occurred in the brain, muscle and salivary gland tissue of the aphid. Most of the particles had one rounded and one flat end and measured about 66 X 175 nm; a few had both ends rounded and were about 335 nm long. No such particles were found in aphids that had fed on virus-free plants. The particles were assumed to be those of raspberry vein chlorosis virus, and the results suggest that it multiplies in its aphid vector and is transmitted in a persistent manner.