In a field experiment, the disease rating of the roots of barley plants suffering from ‘take‐all’ was reduced by application of nitrogen, and by a combined dressing of phosphate and potash. This reduction is attributed to the fact that manuring enables the cereal plant to produce new crown roots more quickly thanOphiobolus graminiscan infect them. In an earlier pot‐culture experiment, operation of this disease‐escape mechanism was inadvertently reduced by inoculating plants at the crown, and by environmental conditions exceptionally favourable to infection (sand culture and relatively high temperatures in the glasshouse). Under these conditions, not only was root disease rating as high in the series receiving a full supply of nutrients (NPK) as in that receiving only one‐third the full amount, but it was reduced almost to one‐half in the series receiving one‐third nitrogen in the presence of full phosphate and potash (PK1/3N). It is concluded that an increase in nitrogen supply may increase the intrinsic susceptibility of individual roots to infection, at the same time as it promotes disease escape and increases yield of