In performing iron tolerance test in hookworm patients, the following results were obtained: 1. In the intravenous iron tolerance test iron requirement by tissues has been found quite high; and this seems to be due to iron deficiency in the erythropoietic system and a greater up-take of iron (iron depot) on the part of viscera. 2. In the iron absorption tests, on the whole the majority of patients show a poor absorption of iron, but after elimination of hookworms their iron absorption returns to the normal or better.