In the investigations carried out for the purpose of determining the vertical migration of hookworm larvae found in the soil of farms where "Wakana disease", the so-called young-green disease occur and numbers of hookworm larvae which adhere to young green leaves in these farms, the following results have been obtained. 1) In the morning and the daytime, more hookworm larvae are found in deeper layers of the soil of the farm where the young green disease is known to occur. 2) In the case there are numerous hookworm larvae in the field where the young green disease is known to occur, naturally more hookworm larvae are found adhering to young leaves growing in the field.