Hydrogenation of dimethyl succinate over monolithic copper and nickel catalysts was studied using a semibatch reactor in which liquid was circulated, while hydrogen was continuously passed through the mixture. Flow rates of both phases were adjusted, so the system operated in the Taylor flow regime. The process was investigated at 150-240 degreesC and 3-7 Mpa. A nickel catalyst was active, but was insufficiently selective. Higher loaded copper catalysts were active and selective with respect to gamma -butyrolactone at relatively low conversions. Catalyst activity (initial rates) was similar to that for the liquid phase hydrogenation of maleic anhydride over conventional catalysts previously reported. The catalysts deactivated, but unlike the nickel catalyst, activity of copper catalyst was easily restored by high temperature treatment in hydrogen.