The intradermal catabolism of antibodies injected in guinea pigs to provoke skin reactions was studied using 125I-labeled guinea pig IgG1 and IgG2 anti-ovalbumin antibodies. Disappearance of both the IgG1 and IgG2 antibodies from injected sites was accelerated by intravenous injection of the antigen. The antigen-antibody complexes produced in vitro were also catabolized more rapidly than free antibodies, when estimated using 125I-labeled antibodies. On the other hand, the catabolism of normal IgG2 was not influenced by local anaphylactic reaction elicited by IgG1 antiovalbumin antibody coexisting at the sites. Therefore, the enhanced catabolism of antibodies on challenge was not caused by increased vascular permeability due to anaphylactic reactions, but by more rapid elimination of immune complexes formed at the sites. The Fc parts of IgG1 and IgG2 antibodies played an essential role in the enhancement of catabolism since the catabolism of the F(ab')2 fragments was not accelerated by complex formation with ovalbumin, but rather reduced.