The lipase from Rhizomucor miehei adsorbed on polymer beads retains substantial catalytic activity even after exhaustive drying, and the use of dry box procedures to prevent entry of atmospheric water. Rates of esterification and transesterification (alcoholysis) were measured while stirred in hexane pre-dried to similar low water activity (aw). The rate of dodecyl decanoate synthesis was over 30% of that at the optimum (aw 0.55) after drying with anhydrous CuSO4 (aw less than 10(-3)) or MgO (aw less than 10(-4). Freshly reactivated molecular sieve could cause a further reduction in, but not elimination of, activity.