The human recombinant S-Lac lectin, L-14-II, produced in an Escherichia coli expression system, has been co-crystallized in the presence of lactose by the hanging drop vapor diffusion method. The crystals grow in space group P2(1)2(1)2(1) with unit cell dimensions of a = 43.6 A, b = 57.8 A, c = 108.2 A, with a dimer in the asymmetric unit. On a conventional rotating anode the crystals diffract to at least 2.8 A resolution.