Crotalaria usaramoensis E. G. Baker affords a new alkaloid usaramoensine, stereoisomeric with senecionine and integerrimine. Usaramoensine gives upon hydrolysis with aqueous alkali retronecine and a new acid, usaramoensinecic acid, stereoisomeric with senecic and integerrinecic acids. By lactonization it gives integerrinecic acid lactone. A careful infrared and ultraviolet absorption study of these acids and alkaloids has permitted the conclusion that usaramoensinecic acid and senecic acid have the same configuration (cis) about the double bond and differ only in the configuration of the asymmetric carbon atom holding the hydroxyl. Integerrinecic acid has the trans-configuration about the double bond and the hydroxyl group cis to the carboxyl with which it lactonizes. On the other hand the alkaloids, usaramoensine and integerrimine, have the same double bond configuration (trans) and senecionine the cis double bond configuration. Rearrangements in configuration of the double bond and of the asymmetric carbon holding the hydroxyl group during saponification of the alkaloids and during lactonization of the acids are discussed. Extraction of Crotalaria incana Linn and Senecio glabellus D. C. yielded integerrimine and senecionine, respectively. © 1953, American Chemical Society. All rights reserved.