Cultured roots of Menispermum dauricum, a rich source of the bisbenzylisoquinoline alkaloid dauricine (1), were fed with l-[U-(14)C] tyrosine, L-[3-(13)C] tyrosine, and [2-(13)C] tvramine independently, and the incorporation of possible early precursors into 1 was studied. The results demonstrated that 1 was composed of four molecules of tyrosine, and that tyramine was specifically incorporated into the isoquinoline portions of 1. The unusual chlorine-containing alkaloid acutumine (3), into which (14)C-labeled tyrosine was also incorporated, was identified as one of the main constituents in the alkaloid fraction from the roots.