The structure elucidation of uncaramine (I), a binary alkaloid derived from gambirine and pseudoyohimbine moieties linked together through a C(lO)-C(21') bond, has been performed mainly using ¹H and ¹³C n.m.r. spectroscopy. The presence of a hydrogen bond between the 9-hydroxy proton and the 4'-nitrogen atom established a preferred orientation of the two halves, the C(11)- C(lO)-C(21 ')-H(21') dihedral angle being ca. 20". A complete assignment for the ¹H n.m.r. spectrum of gambirine (2) is also presented.