V M. ANDREOLl, A. AGNOLI, and C. FAZIO The transfer of a methyl group from a donor to an acceptor compound is a fundamental biochemie al process long since known to biologists; the process is involved, for instance, in the metabolism of porphyrins, nuc1eic acids, and fatty acids. Only recently, however, did transmethylation processes reveal their decisive role in CNS biochemistry - namely with the discovery that such processes are linked with the biogenie amines that have been conc1usively identified as the chemical mediators of neu- ronal transmission and, more broadly, of behavior. The...