[en] A method is described for enhancing the rate of exchange of hydrogen atoms in organic compounds or moieties with deuterium or tritium atoms. It comprises reacting the organic compound or moiety and a compound which is the source of deuterium or tritium in the presence of a catalyst consisting of a non-metallic, metallic or organometallic halide of Lewis acid character and which is reactive towards water, hydrogen halides or similar protonic acids. The catalyst is a halide or organometallic halide of: (i) zinc or another element of Group IIb; (ii) boron, aluminium or another element of Group III; (iii) tin, lead, antimony or another element of Groups IV to VI; or (iv) a transition metal, lanthanide or stable actinide; or a halohalide. (author)