In aqueous solutions, [RuCl2(TPPMS)(2)](2) (TPPMS = 3-sulfonatophenyldiphenylphosphine) catalyzes the exchange between H-2 and D2O or between D-4 and H2O with high efficiency (up to 1 252 turnovers per hour) under mild conditions (298 K, 2 MPa H-2). The exchange rate strongly depends on the solution pH. Similar H/D exchange is observed with the water soluble tertiary phosphine complexes [RhCl(TPPMS)(3)], [RhCl(TPPTS)(3)] and [RuCl2(PTA)(4)] as catalysts (TPPTS = tris(3-sulfonatophenyl)phosphine. PTA = 1,3,5-triaza-7-phosphadamantane) which, however, show lower activity. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.