Alower melting sample of montagnetol has been isolated fromRoccella montagnei. It gives all the reactions of montagnetol, but differs in having a lower melting point and a different crystal structure, and in being dextrorotatory. Hence it is identified asd-montagnetol. The higher melting compound is the racemic variety having no optical activity. The general lesults indicate that racemisation takes place even in the plant.