The isolation from Rauwolfia serpentina of a new alkaloid isomeric with yohimbine and identified as 3-epi-a-yohimbine is reported. Degradative and synthetic evidence demonstrates the presence of the 3-epialloyohimbane ring system. This is confirmed by isomerization of 3-epi-a-vohimbine to α-yohimbine. Neither the alkaloid nor its synthetic esters possess re-serpine-like activity. © 1955, American Chemical Society. All rights reserved.