A simple isolation method for rare actinomycetes belonging to the family Streptosporangiaceae was developed, in which a water suspension of air-dried soil was first treated with chloramine-T (1.0%), a chlorine-releasing biocide, diluted in water, and subsequently cultured on plates of humic acid-vitamin medium. The chlorination treatment significantly inhibited the growth of non-filamentous bacteria and undesirable actinomycete contaminants on the plates, thereby facilitating the selective isolation of bacteria from the Herbidospora, Microbispora, Microtetraspora and Streptosporangium genera.