The water-soluble complexes [{RuCl2(mTPPMS)(2)}(2)], [RuCl2(PTA)(4)], [RhCl(mTPPMS)(3)], [RhCl(mTPPTS)(3)], and [RhCl(PTA)(3)] (mTPPMS=sodium salt of meta-sulfonatophenyl-diphenylphosphine, mTPPTS=sodium salt oftris(meta-sulfonatophenyl) phosphine, and PTA=1,3,5-triaza-7-phosphaadamantane) showed high catalytic activity (up to 1252 h(-1)) in the H-D isotope exchange reactions between H-2 and D2O or D-2 and H2O. The reactions took place at 20-70degreesC, 0.1-2 MPa H-2, and were strongly influenced by the pH. In the hydrogenation (with H-2) of unsaturated acids in D2O, the relative rates of H-D exchange, hydrogenation and deuteration were determined by the individual substrates and catalysts: in the reaction of maleic acid catalyzed by [RhCl(mTPPMS)(3)] only hydrogenation took place with no deuteration and H-D exchange, whereas a similar reaction of itaconic acid was accompanied by a fast H-D exchange and the product methylsuccinic acid was highly deuterated.