The diastereoselective hydrogenation of o-toluidine covalently linked to the chiral auxiliary (S)-proline has been studied. The hydrogenation of (S)-proIine-2-methylanilide on supported noble metal catalysts yielded both the cis and the trans isomers of (S)-proline-2-methylcyclohexylamide. Rhodium and ruthenium were found to be the most active catalysts, rhodium being more selective than ruthenium. With (S)-proline as the chiral auxiliary, the 1R,2S cis-cyclohexanediyl isomer formed preferentially and with (R)-proline the 1S,2R cis-cyclohexanediyl isomer formed. No diastereoselectivity was obtained for the trans isomers. The activity of rhodium catalysts was dependent on the rhodium salt used as a precursor in catalyst preparation and on the support and the process conditions, while the cis-trans selectivity was independent of these parameters. The diastereoselectivity was dependent only on the nature of the noble metal. Prereduced and reused rhodium catalysts were less active than fresh ones. EXAFS and XANES showed that the catalyst was in an incompletely reduced state during the reaction.