A method was developed to reduce the numbers of thermophilic bacteria on isolation plates, which in turn facilitated the detection and isolation of thermophilic actinomycetes. The method involves exposing the test material to bacteriophage suspensions prior to inoculation on isolation plates. This method was applied to composted eucalyptus bark samples, which were then inoculated on R8 and 1/2 TSA + 0.2% casein hydrolysate agar plates. The phage susceptibility of thermophilic bacteria provided a selective means of reducing their numbers on isolation plates and hence increased the numbers ofThermomonospora,Saccharopolyspora rectivirgula, and thermophilicStreptomycesspp. on these media in comparison with the numbers recorded from control plates.Key words: bacteriophage, thermophilic bacteria, thermophilic actinomycetes, composted eucalyptus bark.