A new procedure was developed for enzyme immobilization by entrapment in copper alginate gel. The mechanical properties of the copper alginate gel were characterized and compared with those of the most widely used calcium alginate. The system was applied to the immobilization of a fungal phenol oxidase. Optimal conditions for enzyme immobilization were set up : the system immobilized 85% of the enzyme, and the remaining 15% was recovered in the aqueous immobilization medium. The stability and activity of the immobilized enzyme were studied. After immobilization, the enzyme was active in a wider pH range, the temperature of its optimal activity was shifted to lower values, and the possibility of storage at 4 degrees C was greatly improved. The immobilized enzyme generally increased the rate of oxidation of various substrates. The results indicate a potential use of this system for the construction of bioreactors to be used in the detoxification of polluted waste waters.