The asymmetric hydrogenation of alpha-diketones was investigated over finely dispersed polymer-stabilized and supported platinum clusters. It was shown that the rate-accelerating effect of cinchonidine in this reaction was much less pronounced than the case of Pt/cinchona/alpha-ketoester system. The activity and enantiomeric excess (e.e.) for 3-hydroxy-2-butanone reached maximum when the molar ratio of the modifier to reactant was about 1:650. There was no close correlation between the catalytic performance of the platinum clusters and the polarity of the solvents, whereas good enantioselectivity (> 40%) as well as activity could be obtained in a mixture of dichloromethane and ethanol.