The administration of N-methyl-[2- 14C]-Δ 1-piperideinium chloride to Nicotiana tabacum and N. glauca plants led to the formation of (−)-[2′- 14C]- N-methylanabasine, having the same specific activity as the administered radioactive compound. Radioactive anabasine of lower specific activity was also isolated from these plants. When dl-[2- 14C]-lysine, a well established precursor of anabasine, was fed to these species, negligible activity was detected in N-methylanabasine, which had been added to the harvested plants in order to trap any activity which might have resided in this alkaloid. It is therefore concluded that N-methylanabasine is not an intermediate in the biosynthesis of anabasine from lysine, and its formation in the present work is an example of an aberrant biosynthesis.