Summary: Tissues of actively immunized dogs transplanted by blood vessel anastomosis into hypersensitive recipients show a complete acquired insusceptibility to the hepatic anaphylatoxin. The hepatic anaphylatoxin, therefore, must be regarded as a secondary antigen, presumably of protein nature, and conceivably a denaturization product of the primary antigen. The antianaphylatoxic immunity factor is apparently not transferred from one animal to another by even massive immune blood transfusion.