A lipase from a wild strain of Penicillium citrinum was encapsulated in AOT/isooctane-reversed micelles, and the kinetic parameters were studied relative to triolein hydrolysis. Lipolytic activity was strongly dependent on the water amount in the system (W-o) and presented a bell-shaped curve for this parameter, with a maximum in the range of W-o 10-15. Optimum conditions for enzyme activity were pH 8.0 and 45 degrees C. The influence of substrate concentration was also studied. The enzyme showed a Michaelis-Menten behavior and the apparent kinetics constants were calculated as being V-max.app. = 120 U/mg and K-mapp = 49.2 mM.