It is generally recognized that most drugs and many environmental toxicants are conveyed, following absorption, to their respective sites of action and elimination by the circulating blood. While certain xenobiotics are simply dissolved in serum water, numerous others are associated or bound to blood constituents including albumin, globulins, lipoproteins, and erythrocytes. It has long been accepted that the binding of drugs to plasma albumins is the most significant aspect of drug binding in plasma (Goldstein, 1949; Meyer and Guttman, 1968; Koch-Weser and Sellers, 1976).