A process for the preparation of a hydrogenation catalyst by reduction of platinum in an oxidation stage of not less than 2 in an aqueous medium in the presence of a carboniferous support, optionally following partial poisoning with a sulfur, arsenic, tellurium, or antimony-containing compound, using a reducing agent, in which the reducing agent used is an ammonium or phosphonium salt of the general formula I �XR.sup.4 !.sub.n Y I in which X stands for N or P, R stands for hydrogen, C.sub.1 --C.sub.18 alkyl, C.sub.5 --C.sub.10 cycloalkyl, phenyl radical, and also a C.sub.1 --C.sub.4 alkyl radical substituted by phenyl, the phenyl radicals being mono-to tri-substituted by C.sub.1 --C.sub.6 alkyl, halogen, nitro or amino, if desired, provided that the radicals R may be the same or different but cannot simultaneously denote hydrogen, if X is P, n is an integer of 1 to 3, and Y is an organic anion which can reduce platinum in an oxidation stage other than zero to platinum in the oxidation stage of zero.