GLAUCARUBIN, a bitter lactone found in Simaruba glauca, and used medicinally as an amœbicide, has the empirical formula C25H36O10 and a molecular weight of 496. Its chemical structure is known to be similar to that of chaparrin2 and quassin3. Recently the chemistry of the family Simaroubaceae has been the subject of a considerable number of investigations4,5. Examination of the structure of this compound had been in progress in the Department of Medicinal Chemistry, State University of New York at Buffalo, when it was decided to apply X-ray crystallographic methods to this problem. The crystals of p-bromobenzoate derivative were prepared at this department and the X-ray investigations were undertaken at the Roswell Park Memorial Institute at Buffalo, with the hope that a complete single crystal structural study of this compound would contribute useful information about the chemistry of this class of compounds.