Increased reaction rates and increased enantioselectivities were observed with decreased concentrations of n-alkanols when resolving 2-methyldecanoic acid by esterification catalysed by immobilised lipase from Candida rugosa at controlled water activities in cyclohexane. The enantioselectivity was found to be independent of the water activity in the reaction medium at the n-heptanol concentrations investigated. However, when n-decanol was used as the acyl acceptor, not only the alcohol concentration but also the water activity in the reaction medium, influenced the enantioselectivity. The results obtained showed that the low enantioselectivity seen at a high alcohol concentration could be explained by the alcohol influencing the apparent V-max(S), and V-max(R) differently.