Summary: Dissociation of specifically purified rabbit antiovalbumin into half-molecules, followed by recombination at neutral pH, resulted in a 6 S product, 81% of which was precipitable by antigen. The sedimentation coefficient, precipitability, and shape of the precipitin curve indicated that most of the molecules in the product were bivalent. When the recombination was carried out in the presence of a large excess of dissociated normal γ-globulin, the product did not form specific precipitates with antigen, but specifically inhibited the reaction of ovalbumin with untreated anti-ovalbumin. The results are consistent with univalence of half-molecules of antibody and the previously demonstrated capacity of half-molecules of anti-ovalbumin to combine with halfmolecules of normal γ-globulin, while retaining the integrity of antibody combining sites. A procedure is described for specific purification of rabbit anti-ovalbumin and anti-bovine γ-globulin.