Immunoglobulin composition having a high monomer content, and process for production thereof

An immunoglobulin composition comprising an immunoglobulin, and as an aggregation preventing agent or an aggregate dissociating agent for the immunoglobulin, about 1 to about 600% by weight, based on the weight of the immunoglobulin, of a water-soluble acid additive salt of a basic nitrogen-containing organic compound containing one or more basic nitrogen atoms in the molecule and optionally carboxyl groups in smaller number than the basic nitrogen atoms and having a pKb at 25 DEG C. of not more than 7; and a method for producing an immunoglobulin composition having a high monomer content, which comprises contacting an immunoglobulin in aqueous solution with about 1 to about 600% by weight, based on the weight of the immunoglobulin, of a water-soluble acid addition salt thereby to prevent aggregation of the monomer of the immunoglobulin, and when the immunoglobulin contains aggregated molecules, dissociating the aggregated molecules into monomers, and thereafter, if desired, lyophilizing the resulting product.