The extremely thermostable hybrid Bacillus (1-3,1-4)-beta-glucanase H(A16-M) has been crystallized with polyethylene glycol by vapour diffusion. The single crystals diffract to a resolution of 2.2 A. The protein crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 70.22(7) A, b = 72.56(1) A, c = 49.97(1) A, and has one molecule per asymmetric unit.