Rhodium catalysts supported on a diphenylphosphinated copolymer of styrene and divinylbenzene (SDT) or polyvinylpyrrolidone (PVP) have been tested as catalysts for the heterogeneous carbonylation of methanol in continuous long term vapour phase experiments under mild working conditions (P = 80 bar, T = 180-190 degrees C). While for the SDT-supported catalyst leaching of the rhodium active species occurs, the PVP-supported catalyst, besides excellent activity and selectivity, also shows a very high stability since no detectable rhodium leaching was observed during the experiment (50 h).