<jats:p>The characterization of a new benzylisoquinoline alkaloid, isosevanine, C18H15NO4, m.p. 148° isolated from Hedycarya angustifolia, by a single- crystal X-ray diffraction study is described. Crystals are monoclinic, P21/n, a 22.45(1), b 5.746(4), c 11.569(3) Ǻ, β 93.65(4)°, Z = 4; the structure was refined to a residual of 0.053 for 1016 independent 'observed' reflections.