A previously undescribed virus, probably a new member of the ilarvirus group, was isolated from Parietaria oficinalis showing symptoms of yellow mosaic or mottling. This virus, for which the name parietaria mottle virus (ParMV) is proposed, differs in host range from other ilarviruses. ParMV was purified from Chenopodium quinoa by sap clarification with chloroform, and differential and sucrose density gradient centrifugation. Purified particles were quasi-isometric to ovoid with diameters of about 24, 29 and 36 nm; no bacilliform particles were detected. Buoyant density in caesium chloride, determined on glutaraldehydefixed virus, was 1.35 g/cm3. An antiserum to ParMV was obtained with a titre of 1 : 32 in agar gel double-diffusion tests. ParMV did not react with eight other viruses or virus strains belonging to the ilarvirus group or to pelargonium zonate spot virus. Polyacrylamide gel electrophoresis indicated that ParMV contains a single major protein species of estimated molecular weight 24 300 Da and four RNA species of estimated molecular weight 1.37, 1.19, 0.86 and 0.36 X 10^6 Da.