Conditions for the mono-and di(thiomethy1ation) of N-methyl-3-ethyl-3-phenylpiperidine-2,6-dione and the monothiomethylation of N-methyl-3-(4-aminophenyl)-3-ethylpiperidine-2,~dione, potential inhibitors of estrogen synthetase, are described and contrasted with a closely related lactam, N-methylpiperidone. The influence of solvent, base and electrophile on product distribution is explored.