Electron microscopy of thin sections of diseased raspberry revealed large bacilliform particles c. 430 X 65 nm in plants of Baumforth's B and in an aphid-resistant breeding selection (6820/54), both infected with raspberry vein chlorosis virus but not with other detectable viruses. Particles occurred in the cytoplasm and perinuclear space of a small proportion of xylem parenchyma cells. They had an inner core c. 25-30 nm diam. with crossbanding of periodicity 4.5 nm and were bounded by an outer membrane. They are probably RVCV particles. Plants of cv. Malling Jewel and of a selection (M14), both showing symptoms of raspberry mosaic (veinbanding) disease, contained smaller bacilliform particles c. 125 X 30 nm which occurred singly or in clusters in the cytoplasm of a small proportion of vascular parenchyma cells. It is not known which, if any, of the viruses associated with raspberry mosaic are represented by these particles.