The purification of antibodies in vitro was carried out by adsorbing radioiodinated anti-liver, anti-kidney, anti-lung and anti-spleen sera with a blood vessel fraction or cellular fraction of an organ and then eluting the adsorbed radio-activity by heat at 60°C. It was found that the eluates obtained from blood vessel fractions of liver, kidney and lung had different localizing properties from the eluates of the cellular fractions of the same organs. It was also found that eluates could be prepared which would localize preferentially in either liver, kidney, lung or spleen by purifying the proper anti-tissue serum with a homologous tissue fraction. Antibodies from anti-lung, anti-liver and anti-spleen sera localized to the greatest concentration in the homologous organ when the purification was carried out with the cellular fractions of lung, liver and spleen respectively. With the anti-kidney serum the best results were obtained with the kidney blood vessel fraction.