A total of 331 fungal isolates from container media amended with composted hardwood bark (CHB) were tested for their ability to suppress Rhizoctonia damping-off. Members of the genera Trichoderma, Gliocladium, Penicillium, Mortierella, Paecilomyces, Geomyces and Ophiostoma were among the most effective fungi. Isolates of T. hamatum and T. harzianum, the mostabundant taxa isolated from suppressive container media, were generally the most efficaceous antagonists. However, isolates of Trichoderma and other genera obtained from conducive media were also capable of restoring suppression to heated media (60.degree. C) amended with mature CHB. Induction of suppression by T. harzianum was influenced by the degree of decomposition (age) of the organic component in the container medium. In container media amended with mature CHB, the population levels of T. harzianum increased from 102 colony-forming units (CFU)/g (dry weight) to 103-106 CFU/g (dry weight) after 14 days and high levels of disease suppression were observed. However, similar inoculum levels did not induce suppression in a Canadian peat medium or in media amended with fresh or green CHB even though T. harzianum reached high population levels in these media. The production of contaner media that were consistently suppressive to R. solani required not only the addition of antagonists, but also the introduction of the antagonist into an environment that favored antagonistic activity.