Thiophilic adsorption is useful for the purification of immunoglobulins under mild conditions (e.g., see ref. 1). Although there are several established procedures for the purification of immunoglobulins (2-5), thiophilic adsorption appears thus far to be unique in its capacity to adsorb three major classes of immunoglobulins (and their subclasses) (6-8). Furthermore, in contrast to other affinity purification methods (e.g., see refs. 3,4), recovery of the adsorbed (purified) immunoglobulins from the thiophilic adsorption matrix is accomplished efficiently at neutral pH, without the need for perturbation of protein structure (1). The most important utility of thiophilic adsorption is perhaps its use for the selective depletion of immunoglobulins from complex biological fluids (e.g., calf serum and hybridoma culture media, colostrum and milk) (6,7,9). This latter development has been particularly useful with hybridoma cell culture applications (9,10), and in the investigation of milk-immunoglobulin function during early periods of human infant nutrition (6,7).