Reduction of the fungal community in soil caused by the addition of the fungicide methiram and the antibiotic actidione was accompanied by an intensive development of the community of copiotrophic bacteria. Irrespective of the fungal toxic substances used, there was a particularly conspicuous increase in the numbers of bacteria belonging to fluorescent Pseudomonas, among which three morphologically and physiologically different groups were distinguished. All the isolated strains of Pseudomonas were mycolytic and antibiotic for typical bacteria and actinomycetes; most of them decomposed methiram, but none decomposed actidione. Moreover, propagating rapidly in the presence of methiram were also bacteria from the species Vibrio proteolyticus (Aeromonas prozeolyricus), and in the presence of actidione, bacteria from the species Sporocytophaga myxococcoides. The Vibrio strains, but not those of Sporocytophaga, were also mycolytic, like fluorescent Pseudomonas. Contrary to Pseudomonas, no strain of Vibrio nor of Sporocytophaga was antibiotic for typical bacteria and actinomycetes or able to decompose methiram or actidione.