This study represents an attempt to correlate the low numbers ofAzotobacterin rhizosphere and root-free soils at the Central Experimental Farm, Ottawa, with the incidence of bacterial and actinomycete antagonists of this organism. Wheat, radish, and onion were grown in the greenhouse in two soils varying greatly in fertility and organic matter content, and isolations of bacteria and actinomycetes were made periodically for testing againstAzotobacter. It was found that rhizosphere soil contained greater numbers of microorganisms antagonistic toAzotobacterthan root-free soil. Of the three crops used wheat exerted the least effect. In all the tests numbers of antagonists were greater in the fertile Granby sandy loam than in the infertile Upland sand. The results correlated well with theAzotobacterpopulations in these soils as reported in the first paper of this series.