Chitosanases which catalyze the hydrolytic degradation of chitosan ave to be regarded as important for the extensive carbon and nitrogen recycle which occurs in nature. Chitosanases occur widely in soil microorganisms and in some plants, fulfilling a possible defense role in the latter: Chitosanases may find important industrial application in the utilization of the enormous chitosan and chitin substrates, available from sea-food-processing units, for the generation of the size-specific chitosan oligomers required particularly in pharmaceutical industries. Chitosanases having very diverse characteristics ave known and may be of value in basic studies related to their biological role and the structural elucidation of natural chitosan. (C) 1996 Elsevier Science Ltd.