Decreasing enantioselectivity (E-value) by increasing conversion has been observed in transesterification reactions of secondary alcohols catalyzed by a pure protein formulation of lipase B from Candida antarctica (Novozym 525 F). Addition of a range of enantiopure alcohols caused a temporary increase in selectivity of the transesterification reaction of 3-chloro-1-phenoxy-2-propanol with vinyl butanoate. The corresponding immobilized lipase B, (Novozym 435) showed a similar relationship between the E-value and degree of conversion.