The distribution of fixation of nephrotoxic antibodies and their subsequent exchange among the kidneys and non-renal tissue was studied in two experimental conditions. In the first, radioiodine labeled nephrotoxic gamma globulin was injected into rats which were then united by parabiosis to non-injected isologous rats. In the second, a kidney from a rat injected with labeled nephrotoxic gamma globulin was transplanted to an isologous rat. These experiments showed a continuous dissociation and reassociation of the antibodies following their initial fixation to the tissues. This exchange involved primarily the low avidity and specificity antibody in non-renal tissues and to a lesser extent the more avid kidney fixed antibodies.