Since its introduction into the market in 1971 as an enteric coating, HPMCP^® (hypromellose phthalate) has been demonstrated to be effective by many researchers. It is widely used by the pharmaceutical industry. HPMCP^® has been admitted into the NF, EP and JP. It dissolves at pH 5-5.5 and this property can be controlled by varying the phthalyl content. Two grades of different pH solubility, HP-55 and HP-50, are available. The appropriate grade of HPMCP for a particular purpose should be selected in accordance with its properties and formulations.