Abstract
Strains KV and HZ of radish mosaic virus when centrifuged to equilibrium in caesium chloride gave four bands, although they have only two nucleoprotein components. However, when centrifuged to equilibrium in rubidium bromide, HZ gave only two major bands and KV gave these and several extra small bands, presumably because this strain contains aggregates of 12 particles derived from all 3 components and therefore having different densities from the nucleoprotein components.