Spherical particles, 50-60 mμ, in diameter were found in partially purified preparalions, and also in quick preparations made from plants infected with a virus inducing yellow vein banding in cole (Brassica oleracea var. acephala) . These particles apparently had an icosahedral capsid composed by 92 capsomeres, each with 50-60 A in diameter. Uranyl acetate treatment of these particles revealed a central zone, about 25-30 mμ in diameter, which bound strongly with the stain, indicating that this part of the particle is nucleoprotein. Such particles were absent in healthy plants, but they were detected after these plants were inoculated by tissue union, mechanically, or by aphids with the cole yellow vein banding virus. Similar particles were found in ultrathin leaf sections from cole infected by yellow vein banding virus, invariably embedded in a cytoplasmic inclusion body, but their diameters were slightly smaller (35-45 mμ). These inclusions, with variable dimensions and shape, were composed by an amorphous, dense and granular matrix, and were detectable even under light microscope level in thicker sections. It is likely that the above described virus is related to the cauliflower mosaic virus, due to the similarities in particle morphology and induced diseases.