Chitinase from barley seeds has been crystallized at room temperature using polyethylene glycol as precipitant. The crystal is monoclinic, belonging to the space group P2(1), with unit cell parameters of a = 69.43 A, b = 44.55 A, c = 81.41 A, and beta = 111.95 degrees. The asymmetric unit seems to contain two molecules of chitinase with a corresponding crystal volume per protein mass (VM) of 2.25 A3/Da and a solvent content of 45% by volume. The crystal diffracts to at least 2.0 A with X-rays from a rotating anode source and is very stable in the X-ray beam. X-ray data have been collected to better than 2.2 A Bragg spacing from a native crystal.