According to a previous study, alcohol concentration influences the enantiomeric ratio and initial rate of Candida cylindracea lipase-catalyzed enantioselective esterification of racemic 2-(6-methoxy-2-naphthyl) propionic acid in microaqueous isooctane in a similar manner. Such an influence might be attributed to the different water partitioning coefficients. in this work, we performed enzymatic resolutions in controlled water activity atmospheres, thereby separating the influence of alcohol concentrations from the effect of water partitioning. Despite this constant water activity condition, a similar dependence of enantiospecificity and initial rate on the concentration of acyl acceptor (n-butanol) was also found. This finding suggests that the alcohol concentration influences enzyme performance, but not because it strips water from the enzyme. The unexpected observations imply that an undetermined factor must be considered when the enzymatic resolution is performed in nonconventional media. (C) 2000 Elsevier Science Inc. All rights reserved.