A new member of the naphthalene-isoquinoline series of alkaloids, ancis-trotectorine (2), has been isolated from the leaves of the Thai medicinal plant Ancistrocladus tectorius (Ancistrocladaceae). The structure was deduced through single crystal X-ray crystallography and complete 1H-nmr spectroscopic assignments were made. Ancistrotectorine (2) is the second member of the 7, 3'-linked naphthalene-isoquinoline alkaloid group to be isolated. © 1985, American Chemical Society. All rights reserved.