A metastasis-inducing protein, human S100A4, cDNA was overexpressed in Escherichia coli. The recombinant protein was purified by three chromatographic procedures. Crystals were obtained using polyethylene glycol as a precipitant. The native S100A4 crystals did not diffract sufficiently well for data collection, but the SeMet S100A4 crystal, grown using similar conditions as for the native, was found to be stable during exposure to X-rays and diffracted to 4 A resolution in-house. The crystal belongs to space group P6 or P3. The unit-cell parameters are a = b = 47.1, c = 175.6 A, alpha = beta = 90, gamma = 120 degrees. Complete data will be collected using synchrotron radiation.