Water adsorption isotherms of pure lipases A and B from Candida rugosa are different and can be used to distinguish between the isoenzymes. The maximum esterification yield (50%, 20 h) can be achieved at initial 0.9 < a(w) < 1.0. Lipase B is more stereoselective (49% yield, 98% enantiomeri excess) than lipase A (47% yield, 72% enantiomerci excess) but both isoenzymes mainly esterify the (S) 2(4-isobutylphenyl)propionic acid (Ibuprofen).