1. Laboratory experiments have shown that solutions of ferric chloride, ferrous sulphate and chinosol, in sufficient concentration, have a lethal action on the larvae of H. schachtii. The vapours given off by potassium ethyl xanthate were also found to be lethal.2. Each of these four chemicals was mixed with moist infected soil and the mixture left for a period. When the cysts were separated and placed in a solution of potato-root excretion, the numbers of larvae which hatched were reduced as a result of the chemical treatments, in the order: potassium ethyl xanthate, ferric chloride, chinosol, ferrous sulphate.3. When ferric oxide was placed in a solution of root excretion containing cysts, the commencement of hatching was delayed.4. Experiments on a very small field scale were carried out, the chemicals being applied chiefly to the rows in which potatoes were planted. The plants growing on the treated areas did not, in general, show marked symptoms of root-eelworm infection as did those on the control areas.5. The yields of potatoes from each row are tabulated. The highest yields were obtained following the treatment with ferric oxide.