D-Fructose and D-fructose/D-glucose mixtures have been hydrogenated in water at 60-510" and 20-75 atm. of hydrogen with Ni, Cu, Ru, Rh, Pd, OS, Ir, and Pt severally as catalysts. The selectivity for the formation of D-mannitol from Dfructose as well as the selectivity for the hydrogenation of D-fructose in the presence of D-glucose with Cu/silica as the catalyst are substantially higher than those for the other catalysts. With Cu/silica as the catalyst, the hydrogenation of D-fructose is first order with respect to the amount of catalyst and the hydrogen pressure, whereas a shift from first-to zero-order kinetics occurs on going from low (<0.3M) to high (>O.~M) concentrations of D-fructose. D-Fructose is preferentially hydrogenated via its furanose forms, presumably by attack of a copper hydride-like species at the anomeric carbon atom with inversion of configuration. Preferential adsorption of pyranose with respect to furanose forms occurs, whereas the furanose forms show a much higher reactivity. The mechanism proposed for the copper-catalysed hydrogenation reaction explains both the enhanced yield of D-mannitol from boric esters of D-fructose and the diastereoselectivity of the hydrogenation of seven other ketoses.