Abstract: The present invention is directed to a process for the catalytic hydrogenation of a starting material containing 4,4'-diamino-diphenylmethane (4,4'-MDA) or its mixtures with 2,4'-diamino-diphenylmethane, 2,2'-diamino-diphenylmethane and/or higher ring compounds of the diphenylmethane series to a hydrogenation product having a trans-trans isomer content of 4,4'-diamino-dicyclohexylmethane (4,4'-HMDA) of about 15 to 40 weight percent, based on the diamine content of the hydrogenated product, by continuously hydrogenating in at least one fixed bed reactor at a temperature of about 100.degree. to 190.degree. C. and a pressure of about 50 to 350 bar in the presence of a ruthenium catalyst on a catalyst support having a BET surface area of about 70 to 280 m.sup.2 /g and an average pore diameter d.sub.p of about 10 to 320 .ANG., the catalyst being prepared by impregnating the catalyst support to a penetration depth of at least about 50 .mu.