Studies are conducted of reactions in which methyl groups are transferred, with and without the agency of enzymes, the former serving as catalytic reactions for which the latter will constitute standards. The comparison will provide measures of catalytic acceleration. Mechanistic studies, including kinetic isotope effects will reveal the structures of the transition states for both reactions. Th data will serve as fundamental information for the synthesis of transition-state analog inhibitors for these enzymes, which are important in the function of the brain and other parts of the nervous systems, in the defensive apparatus of the intestinal wall and in the action of the liver. Drugs which may be designed with information in this catagory should be ultrapotent and specific.