The shape of the profiles of enzyme activity versus water activity for four different lipases were independent of the reaction used to determine the activity. The profile for each lipase (Rhizopus arrhizus, Pseudomonas sp., Candida rugosa and Lipozyme) in esterification, hydrolysis and transesterifications profiles were the same. In transesterification the yield was unaffected by the water activity but the hydrolysis yield increased with increasing a(w).