Bacteria with possible relevance to the growth of the take-all fungus were counted from surfaces of lesioned and healthy roots of wheat growing in soil from a field monoculture system. Numbers showed short-term seasonal and long-term monocultural changes, which seemed to be genuinely associated with the monoculture. Bacteria were more numerous on lesioned than healthy roots. Only bacteria inhibitory to growth of Gaeumannomyces graminis on agar and Pseudomonas spp showed consistent changes irrespective of the source of the roots. Relationships were considered between the microflora on lesioned tissue and (a) severity of disease on roots supplying the lesions, and (b) infection produced on axenic seedlings inoculated with the lesioned tissue. Only total bacterial counts on the lesions from tillering and mature plants were positively correlated with disease on the donor roots. Only inhibitory bacteria on lesions from tillering and mature plants were positively correlated with disease on test seedlings. Pseudomonas spp showed no correlations. Interpretation of data differed with age of plant and the sequence in the monoculture from which plants or soil came.