An experiment was set up to investigate the effect of root diffusates from different varieties of potatoes on natural infestations of cysts in three different soils. A series was included in which no root diffusate at all was used, to obtain an estimate of the degree of spontaneous hatching which occurred. In the absence of diffusate, about 50 per cent, of larvae emerged from the cysts, as compared with 84 per cent, in the case of soils treated with diffusates. Significant differences were detected in the degree of emergence under the action of the different diffusates, that from “Ulster Chieftain” having the greatest effect. Significant differences were also detected between the different soils, larval emergence being lowest in the greensand.