A disease of water dropwort, characterized by yellows and stunting of the plants, was found in Kanazawa City, Ishikawa Prefecture in 1980. Electron microscopic studies revealed the presence of numerous mycoplasma-like organisms (MLOs) in the phloem tissues of diseased plants. Both the disease and garland chrysanthemum witches' broom, collected at neighbouring field, were transmitted by Macrosteles orientalis Virbaste. Of 25 species of plants in 14 families, which were inoculated by the leafhopper, 23 plants were infected with the MLOs. The two MLO diseases had the same wide host range similar to that of sickle hare's ear yellows.