The removal of ammonium sulfate from the bulk product of fermented antitoxic serum by continuous diafiltration was not accompanied by changes in the stability of the solution. To concentrate immunoglobulin, eluted from DEAE cellulose, by diafiltration, the stabilization of the solution by adding sodium chloride at high concentration was necessary. The use of membranes purchased from different manufacturers and having similar selectivity characteristics permitted obtaining transfer factor preparations somewhat differing in their biological activity. The process of ultrafiltration, carried out in the atmosphere of compressed carbon dioxide, made it possible to obtain such preparations from donor blood plasma.