A cytosolic chitinase (20 kDa by SDS-PAGE) was partially purified from Neurospora crassa. Linear kinetics for enzyme activity were obtained using the substrate [3H]-labelled regenerated chitin, the preparation yielding an apparent Km of 0.965 mg ml-1 and a Vmax of 3.83 micrograms GlcNAc min-1 (mg protein)-1. The enzyme was highly sensitive to allosamidin, an inhibitor of insect chitinase, exhibiting an IC50 of 1.6 microM. Unlike other chitinases that are inhibited by allosamidin, the mode of inhibition of the N. crassa enzyme was shown to be non-competitive.