Aluminum in the form of aluminum hydroxide, aluminum phosphate or alum has been commonly used as an adjuvant in many vaccines licensed by the US Food and Drug Administration. Chapter 21 of the US Code of Federal Regulations [610.15(a)] limits the amount of aluminum in biological products, including vaccines, to 0.85 mg/dose. The amount of aluminum in vaccines currently licensed in the US ranges from 0.85-0.125 mg/dose. Clinical studies have demonstrated that aluminum enhances the antigenicity of some vaccines such as diphtheria and tetanus toxoids. Moreover, aluminum-adsorbed diphtheria and tetanus toxoids are distinctly more effective than plain fluid toxoids for primary immunization of children. There is little difference between plain and adsorbed toxoids for booster immunization. Aluminum adjuvants have a demonstrated safety profile of over six decades; however, these adjuvants have been associated with severe local reactions such as erythema, subcutaneous nodules and contact hypersensitivity.