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. It was shown; that CHEMS was potent inhibitors of acetylcholinesterase and it alone or in combination with tetrahydroaminoacridine could be used in the treatment of organophosphate poisoning and Alzheimer's disease. It was also revealed, that CHEMS upon incorporation into the cell membrane, which presumably promotes the expression of latent tumor-associated antigens, induced a marked increase in specific immunogenicity of tumor cells.