The lung symptoms of Wakana disease are considered largely caused by the irritation of hookworm larvae migrated into the lung. With the purpose of killing the hookworm larvae, an anchylostomocidal experiment was conducted in vitro with chloroquine diphosphate, Stibnal, Mapharsen, Atebrin and emetin hydrochloride, and the following results were obtained. 1. At the in vitro concentrations comparable to those attained for adults, chloroquine diphosphate showed a most pronounced anchylostomocidal effect upon Anchylostoma caninum larvae followed by Stibnal, Mapharsen, Atebrin and emetin hydrochloride in that order. 2. The first three drugs found to be more effective against hookworm larvae in the above experiment were tested for the anchylostomocidal effect on Dubini larvae by adding the serum obtained from normal persons given intravenous injection of the adult dosage of these drugs. In this experiment, too, chloroquine diphosphate was most effective followed by Stibnal and Mapharsen. 3. From these results, it appears that chloroquine diphosphate, Stibnal and Mapharsen act quite effectively as auchylostomocides against hookworm larvae, and good therapeutic effects of these drugs can also be expected when used in Wakana disease. Of these three drugs, chloroquine diphosphate was most effective in both experiments and together with a possible high concentration of intravenously injected chloroquine diphosphate in the lung, the agent is considered to be a drug of choice in the treatment of Wakana disease.