Cholesteryl hemisuccinate (CHEMS) is an acidic cholesterol ester. It self assembles into bilayers in alkaline and neutral aqueous media. CHEMS exhibits pH sensitive polymorphism. It consists of succinic acid esterified to the beta-hydroxyl group of cholesterol. This chemical modification results in the ability of CHEMS to adopt a lamellar assembly in suitable aqueous media, whereas cholesterol forms monohydrate crystals in an aqueous environment.