The intent of this study was to determine what influence, if any, increasing age has on the binding of drugs by plasma proteins. Plasma from healthy subjects ranging in age from 21 to 94 years was used. The binding of phenytoin (diphenylhydantoin) (acid), penicillin G potassium (benzylpenicillin potassium), and phenobarbituric acid was determined by equilibrium dialysis of 14C-labeled compounds. No differences were found in total protein concentration; however, albumin was reduced in subjects over 50 years of age. Plasma binding of each drug studied was not related to age; this finding suggests that age per se is not a factor in the binding of drugs by plasma proteins.