(3H)-labeled indicine N-oxide, indicine, retronecine, and retronecine N-oxide have been chemically synthesized for use in biological studies. The synthesis of (3H) indicine N-oxide proceeded from incidine N-oxide through a process involving reduction to indicine, ester cleavage, oxidation of the exocyclic carbon on the pyrrolizidine moiety, reduction with lithium aluminum tritide, re-esterification, and re-oxidation to the N-oxide. In the subsequent biological studies, the enzymatic, anaerobic reduction of indicine N-oxide to indicine has been demonstrated, and studies on the microsomal oxidation of (3H)indicine and (3H)retronecine to activated derivatives have been performed.