An extracellular chitinase of Bacillus sp. WY22 was purified by 9.6-fold. It had a Mr of 35 kDa, an apparent K-m value for colloidal chitin of 3 mg ml(-1) and was optimally active at 37 degreesC and pH 5.5 over 1 h. The enzyme could also hydrolyse swollen chitin, glycol chitin and chitosan with relative activities of 76%, 34% and 23% compared with colloidal chitin. It formed chitotriose as a major product from colloidal chitin and glycol chitin.