1. Guinea pigs injected intravenously with massive doses of India ink before active sensitization exhibited occasionally a more or less marked, decreased sensitiveness to the reinjection of the antigen.
2. The serum of rabbits which had received massive doses of India ink before the sensitizing injections, showed approximately the same titer of anaphylactic antibodies as that of sensitized normal control animals, as demonstrated by the degree of passive sensitization induced in guinea pigs.
3. The precipitin titer of sensitized rabbits blocked with massive doses of India ink was somewhat lower than that of sensitized normal controls. In one instance, the intravenous injection of smaller doses of India ink was followed by a higher precipitin titer. No uniform relation was found between the height of the precipitin titer and the anaphylactic power of the antiserums.
4. One blocking injection of India ink given to guinea pigs before passive sensitization did not interfere with the occurrence of anaphylactic shock nor alter its nature.