Abstract: Dental and medical instruments and appliances are chemically sterilized by immersion in or subjection to a formulation or composition comprising as active antimicrobial agents a combination or admixture of an iodophor such as the povidone-iodine complex or a quaternary ammonium compound such as cetyl pyridinium chloride and a peroxide such as H.sub.2 O.sub.2, the antimicrobial action of the iodine derived from the iodophor being enhanced or potentiated by oxygen released from the peroxide. The invention is applicable also to the chemical sterilization of surgical sites. Procedure for making and using the sterilizing formulation or composition is described.