Continued fractionation of the polar constituents of Adina rubescens has yielded, in addition to those already reported, a new indolic glucoside, rubescine. Structure (la) is proposed for rubescine on the basis of chemical (including methylation, catalytic hydrogenation, acetylation, Zemplen deacylation) and spectroscopic (UV, CD, n.m.r., mass spectra) evidence. Zemplen deacylation of rubescine gave a quantitative conversion to the known vincoside lactam (3a) and methyl 3,4-dihydroxycinnamate (caffeate), indicating rubescine is vincoside lactam esterified on the glucose moiety by caffeic acid. Detailed n.m.r. analysis, particularly 220 MHz spectra of tetrahydrorubescine, determined the location of the caffeoyl substituent on the glucose residue, leading to the establishment of the complete structure (la).