Studies were carried out using mice as experimental hosts to detemine whether immunity can be established against Ancylostoma caninum, and the following results were obtained;
1) The mortality of the mice, infected with the larvae of A. caninum, depended upon the numbers of larvae.
2) Mice infected with 300, 700, and 1, 500 larvae orally at the intervals of 6 days and 15 days showed a resistance to challenging infection of 5, 000 larvae orally.
3) In mice, immunized with previous infection and remarked no protection to challenging infection, less numbers of larvae were detected from organs of the body than from those of non-immunized control.