Anti-Salmonella pullorum and anti-Brucella abortus sera produced in hedgehog, rat, rabbit, guinea-pig and ox were fed to young suckling hedgehogs. Anti-Salmonella agglutinins are absorbed far more readily than anti-Brucella agglutinins, with the exception of those produced in the guinea-pig which have a comparable rate of entry via the gut to the circulation. Homologous anti-Salmonella agglutinins are absorbed more readily than those from other species. No detectable passage of agglutinin occurred from hedgehog anti-Brucella serum produced as a result of a single immunizing injection, whereas some passage occurred from hyperimmune hedgehog serum of similar titre. Thus the gut of the young hedgehog is capable of showing a selection between antibodies produced in the same species in response to the same antigen. The gut also exhibits selection between antibodies produced in the same species in response to different antigens. These facts, and the closely related information on the capacities of the gut of the young rat, are discussed in relation to the location of antibodies among the serum proteins and the species in which the antibodies were produced.