The effects of reaction variables (temperature, pressure, solvent type, substrate to catalyst ratio and substrate concentration) on enantioselectivity of methyl acetoacetate hydrogenation were studied. Raney nickel modified with (2R,3R)-(+)-tartaric acid was used as a catalyst. The reactions were carried out in a liquid phase, under atmospheric and increased hydrogen pressure. It was found that the reaction variables have a significant effect on the resulting enantioselectivity. Adecrease of enantioselectivity either occurred at low substrate concentration in the reaction mixture or related to a catalyst. Changes of enantioselectivity were monitored during the reaction. The highest values of enantioselectivity were achieved under high hydrogen pressures (10 MPa), at a temperature of 60 degreesC and with tetrahydrofuran as the solvent. (C) 2002 Elsevier Science B.V. All rights reserved.