Recombinant amylosucrase from Neisseria polysaccharea was crystallized by the vapour-diffusion procedure in the presence of polyethylene glycol 6000. The crystals belong to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 95.7, b = 117.2, c = 62.1 A, and diffract to 1.6 A resolution. A p-chloromercuribenzene sulfonate (pcmbs) derivative has been identified and a selenomethionine-substituted protein has been produced and crystallized.