Southern bean mosaic virus (SBMV) is the archetype of group sobemovirus, which also includes turnip rosette virus (TRoSV), cocksfoot mottle virus, rice yellow mottle virus, and sowbane mosaic virus. SBMV, a pathogen of cultivated legumes, is widespread in the tropical and warm temperate parts of the world. SBMV virions are punned by precipitation with 4 to 8% polyethylene glycol, acid clarification, and differential centrifugation. SBMV virions are spheroidal. By electron microscopy they measure 30 nm in diameter, a value which agrees with the data obtained from X-ray diffraction and neutron scattering studies. SBMV interacts strongly with a lipid composite of phosphatidylcholine, cholesterol, and stearylamine, which forms a uniform 5-nm thick shell around the individual virions. Native SBMV is stable in the presence of protein denaturants and enzymes, indicating a highly integrated and coordinated macromolecular organization.