The readily reducible double bond of gelsemine has been shown to be present in a vinyl side chain and not in an exocyclic methylene group as had been previously assumed. Oxidation of the olefinic double bond in N(a)-methylgelsemine with sodium metaperiodate in the presence of a catalytic amount of osmium tetroxide gave an aldehyde having one carbon less than the starting material. That the product was an aldehyde and not a ketone was proved (a) by conversion to an oxime which was readily dehydrated to a nitrile, and (b) by Wolff-Kishner reduction to a compound containing a C—CH3 group not present in the aldehyde itself.