A reusable protein seed crystal processed by chemical cross-linking is developed. The process used to achieve cross-linking with glutaraldehyde is described. The lattice constants of the resulting crystals were analyzed using X-ray diffraction, and the characteristics of the seed crystals were investigated using an optical microscope and an atomic-force microscope. The results showed that the lattice constants of the crystalline layer that developed on the cross-linked crystal are identical to those of the as-grown crystal. The layer that grows on the cross-linked seed crystal maintains the same crystallographic direction as the cross-linked crystal. Also, the surface morphology of the crystalline layer is the same as that of the as-grown crystal. Since the cross-linked seed crystals do not dissolve in undersaturated solution, they can be repeatedly used for crystal growth experiments. (c) 2004 Elsevier B.V. All rights reserved.