The fungus Rhizoctonia solani Kühn and the root-lesion nematode Pratylenchus minyus Sher & Allen were closely and consistently associated in naturally occurring infections of winter wheat. The resultant root rot was characterized by markedly yellowed and stunted patches of plants in the wheat fields during spring growth. In greenhouse and field experiments the combined effects of the fungus and the nematode upon growth of the wheat was almost twice as great as the effect produced when either pathogen was controlled by a selective soil treatment. By pure culture techniques it was not possible to show that in the penetration of wheat roots the fungus was dependent upon the nematode or that the converse was true.