The isolation of ancistrobrevine B, a new naphthylisoquinoline alkaloid from Ancistrocladus abbreviatus, is described. Elucidation of the complete structure, including the absolute configuration at the two stereogenic centres and the axis, was achieved by chemical and spectroscopic methods. Ancistrobrevine B exhibits a hitherto unprecedented 5,8'-coupling type. The known alkaloids ancistrocladine, hamatine and dioncophylline A were also isolated for the first time from this species.