A potyvirus, for which the provisional name of Amazon lily mosaic virus (ALMV) is proposed, was isolated from an Amazon lily plant (Eucharis grandiflora) with mosaic disease. ALMV which was mechanically transmitted to E. grandiflora induced mosaic symptoms on leaves and flower stalks and tiny etched flecks along the veins of flower petals. Necrotic lesions appeared on inoculated leaves of Chenopodium quinoa and C. amaranticolor, but no systemic infection occurred. ALMV systemically infected Nicotiana benthamiana and induced mosaic symptoms. Other 38 plant species in 12 families tested were not infected with ALMV. ALMV was transmitted non-persistently by aphid (Myzus persicae). The particle length was about 760nm. Pinwheel inclusions were observed in the cytoplasm of the mesophyll cells of infected E. grandiflora plants. The virus was purified from inoculated leaves of C. quinoa by sedimentation with polyethylene glycol 6000 and isopycnic centrifugation in Cs₂SO₄. The purified virus showed an ultraviolet absorption profile typical of a nucleoprotein with a maximum at 260nm and a minimum at 246nm. The A₂₆₀/A₂₈₀ ratio was 1.32. The virus particles contained a single species of single stranded RNA of Mr 3.32×10⁶, and single polypeptide of Mr 35, 000. ALMV was serologically distantly related to Alstroemeria mosaic virus, Hippeastrum mosaic virus, Hyacinth mosaic virus, onion yellow dwarf virus, Ornithogalum mosaic virus, potato virus Y, watermelon mosaic virus 2 and zucchini yellow mosaic virus.