The present invention relates to a process for the hydrogenation of an imines with hydrogen in the presence of iridium catalysts. In particular, the present invention relates to a process for the hydrogenation of imines with hydrogen under elevated pressure in the presence of an iridium catalyst and with or without an inert solvent, wherein the reaction mixture comprises a phosphonium chloride, bromide or iodide in the presence of an acid, which can be an organic or inorganic acid soluble or insoluble in the reaction mixture. Suitable imines are especially those that contain at least one group. If the groups are substituted asymetrically and are thus compounds having a prochiral ketitine group, it is possible in the process according to the invention for mixtures of optical isomers or pure optical isomers to be formed if enantioselective or diastereoselective iridium catatalysts are used.