Nucleocapsids (Nc) of northern cereal mosaic virus (NCMV), a plant rhabdovirus, were isolated directly from infected wheat leaves by including Triton X-100 before the first high-speed centrifugation, which was followed by sucrose density gradient centrifugation and CsCl equilibrium density gradient centrifugation. Purified Nc had a tubular structure with a diameter of 28 nm and a pitch of 5.5 nm with uranyl acetate staining. Gel electrophoretic analysis revealed that Nc consisted of N protein with MW 47 .times. 103 daltons and an RNA with MW 3.5 .times. 106 daltons; intact virions contained in addition 2 major and 1 minor polypeptide with MW 63 .times. 103, 19 .times. 103, and 88 .times. 103 daltons, which probably correspond to G, M, and L proteins, respectively. Antiserum produced against purified Nc had a titer of 1/1024 determined with Ouchterlony gel double diffusion tests. With the enzyme-linked immunosorbent assay, purified Nc was detectable at a concentration as low as 2 .times. 10-5 A260/nm units per milliliter, which corresponds to approximately 10 ng/ml. In vivo-Nc was detected from the homogenates of fresh, frozen and freeze-dried diseased leaves diluted up to 10-5 and also from the homogenates of fresh, frozen and freeze-dried diseased leaves diluted up to 10-5 and also from the homogenate of a single viruliferous planthopper, Laodelphax striatellus.