The use of specific insoluble absorbants as adjuncts for the purification of antibodies (1), enzymes (2), and ribonucleic acids (3) has been demonstrated. The basic approach has been to link a water-insoluble polymer (polystyrene, cellulose, etc.) covalently to a specific molecule (substrate, competitive inhibitor or antigen) which will form a complex with the substance (enzyme, antibody, etc.) being purified in a subsequent column chromatographic procedure. The studies reported here are concerned with the utilization of a specific soluble macromolecular complexing agent in the purification of beef heart lactic dehydrogenase (BH-LDH). The complexing agent (BSA-I) is bovine serum albumin linked covalently to oxanylic acid, which is a competitive inhibitor for the binding of substrate to the active site of the enzyme. The complexing agent (BSA-I) was found to specifically alter the solubility of BH-LDH in ammonium sulfate solution, and the formation of the complex was also shown to be NAD + dependent.