Experimental evidence (measured by NMR) is given for the correlation between the solution-state concentration of the nucleophilic 1:1 modifier-substrate complex and the ee on enantioselective hydrogenation of ketopantolactone using Pt-ss-isocinchonine chiral catalyst. The relationship displays a saturation-type curve, which may indicate an underlying adsorption process involving the catalytically relevant nucleophilic complex. (c) 2008 Elsevier Inc. All rights reserved.