Leaf extracts containing maize mosaic virus (MMV) were purified by treatment with activated charcoal followed by filtration through Celite. Virus was concentrated from the filtrate by sedimentation onto a sucrose pad and then further purified by centrifugation in a 20--50% continuous sucrose density gradient. Buoyant density of virus particles in sucrose solution was 1.181 g/ml. Nucleic acid extracted from virus preparations reacted with orcinol and behaved like RNA in Pederson's diphenylamine test. It was digested by pancreatic RNase and apparently is single-stranded RNA. Virus preparations also contained lipids. The morphology and constituents of MMV particles are therefore those expected for a rhabdovirus.