Actinomycetes, bacteria and fungi were isolated from the rhizosphere of healthy tomato plants grown in soil samples from three organic and three conventional farms. Total numbers of actinomycetes and fluorescent pseudomonads, proportions of cellulolytic and hemicellulolytic actinomycetes, starch hydrolysing bacteria, and chtinolytic fungi, and the diversity of actinomycetes (Shannon-Weaver index) were higher in organically than conventionally managed rhizosphere soil. However, starch hydrolysing actinomycetes and fungi were more numerous in soil from conventional than from organic farms. Functional groups of actinomycetes and bacteria but not of fungi were more similar among samples with the same soil management than between different soil management types. There were significant positive correlations of total numbers of actinomycetes and fluorescent pseudomonads, proportions of cellulolytic actinomycetes and chitinolytic fungi, and actinomycete diversity with suppression of corky root of tomato. Thus, the greatest differences between organically and conventionally managed soils were encountered in actinomycete populations.