Summary: The offspring of antitoxic immune guinea pigs gave anaphylaxis when injected intravenously with toxin-containing material thirty to sixty days after their birth. Sufficient controls were made on the possibility of participation of non-toxin antigens and of non-antitoxin antibodies to justify the conclusion that the anaphylaxis was due to reaction between the toxin antigen and the placentally transmitted antitoxin. The advantage of the use of carefully selected offspring was demonstrated by the high degree of completeness of non-reactivity to non-toxin diphtheria antigens that was exhibited by the offspring of individual mothers whose serum contained none or only small amounts of diphtheria antibodies other than antitoxin. Apart from the question of toxin anaphylaxis the present demonstration of anaphylaxis to diphtheria material on the part of the offspring of immune guinea pigs is of interest as an example of placental transmission of hypersensitiveness to an antigen of bacterial origin.