The rare actinomycete Actinomadura viridis was efficiently isolated from a variety of field soils by a new plate culture method in which a water suspension of dry-heated (110 degrees C, 1 h) soil was treated with 1.0% phenol and cultured on Humic acid-vitamin agar supplemented with kanamycin, josamycin, lysozyme and nalidixic acid. The method significantly eliminated unicellular bacteria and undesirable actinomycetes contaminants from the isolation plates, thereby achieving the highly selective isolation of A. viridis.