Methyl vitamin B₁₂ is shown to be capable of transferring methyl groups to Hg^II, Tl^III, Pt^II, and Au^I; two different reaction paths are involved, one of which, with Hg^II or Tl^III, is an acid-base reaction while the other is probably an oxidation-reduction reaction for it requires both Pt^II and Pt^IV, or Au^I and Au^III.