The aim of this paper is to clarify the confusion that exists in the literature with regard to the asymmetric hydrogenation of keto-carboxylic acids and their esters over Pt-cinchonidine catalysts. It has come to our attention that in many cases incorrect correlations between the absolute configuration and the sign of optical rotation of the product of the hydrogenation reaction-2-hydroxycarboxylic acid and their esters-are given in the literature. The correct correlation is (-)-rotating 2-hydroxycarboxylic acids and their esters have the R-configuration, and (+)-rotating have the S-configuration. (C) 2003 Elsevier B.V. All fights reserved.