The formation of complexes between different proteins, undergoing heat denaturation together was greatly influenced by the presence of salts. It led to changes in serological behaviour of the proteins. The efficiency of different salts in promoting the complex formation, expressed as the reciprocal of the lowest effective concs., followed Hardy''s law. Ions of higher valency were much more effective than those of lower valency. On the alkaline side of the isoelectric point of the proteins the efficiency of salts was detd. by the valency of the cations, and on the acid side by the valency of anions.