Endophytic actinomycetes were isolated from field-grown rhododendron plants for selecting candidates for biological agents to control plant diseases. A spore suspension of R5 (1 ml) was inoculated into a 300-ml flask containing 100 ml of seed medium composed of 1g soluble starch, 0.5g glucose, 0.3g NZ-case, 0.2g yeast extract, 0.5g tryptone, 0.1g K₂HPO₄, 0.05g MgSO₄.7H₂O, and 0.3g CaCO₃ (pH 7.0). The seed culture was incubated for 3 days at 30 ℃ on a rotary shaker (200rpm). A 3-ml aliquot of the culture was added to each of 12 flasks containing 100 ml of production medium composed of 0.5g glucose, 2g glycerol, 2g soluble starch, 1.5g Pharmamedia (Traders Protein, Memphis, TN, USA), 0.3g yeast extract, and 0.1g Diaion HP-20 resin (Mitsubishi Chemicals, Tokyo, Japan); it was then incubated on a rotary shaker (200rpm) at 30 ℃ for 6 days.