The influence of reductive and oxidative heat treatment on the enantioselectivity of chirally modified Pt/alumina has been reinvestigated, using the hydrogenation of ketopantolactone as a test reaction. Enhancement in ee by 39-49% has been observed after treatment in hydrogen at 250-600 degrees C, as compared to untreated or preoxidized catalysts. The changes in ee after reductive and oxidative treatments are reversible, and always the final treatment is decisive. A HRTEM study indicates that adsorbate-induced restructuring of Pt crystallites during hydrogen treatment at elevated temperature can play a role in the selectivity improvement, but the changes are superimposed by the strong structure-directing effect of the alumina support. The possible contribution of other effects (complete reduction of Ptn+ surface species, removal of impurities, or change of Pt particle size) could be excluded.