Summary: Antidextrans produced by rabbits resemble corresponding human antidextrans. Inhibition data indicate that most of the combining regions of antibody in the rabbit sera studied are complementary to chains of not more than five or six hexose units. Dextrans known to contain a high proportion of 1,2-linkages cross-react 85 to 100% with human and rabbit antibodies to dextran 1424, which has an unknown content of 1,2-linkages, thus confirming previous immunochemical inferences that this dextran is also highly 1,2-linked. Inhibition data also support this conclusion.