The presence of alkaloids in the American tropical legume Cassia excelsa Shrad. has been noted by investigators of the U. s. Department of Agriculture and an alkaloid characterized by crystalline salts has been isolated by Brazilian workers. A crystalline alkaloid, C19H37NO2, has been isolated from Cassia excelsa Shrad. and named cassine. The functional groups are identified as a hydroxyl group, a secondary amine, and a methyl ketone. Dehydrogenation of cassine produces a 2,6-dialkyl-3-hydroxypyridine, and cleavage of ketone VI by a second-order Beckmann rearrangement demonstrates the 2-alkyl group to be methyl. These observations and deductions from the n.m.r. spectrum show III to be the structure of cassine.