The human gene coding for the enhancer of rudimentary homologue (ERH) protein was overexpressed in Escherichia coli. The ERH protein was purified by anion-exchange, hydrophobic interaction and gel-filtration chromatography. Well diffracting single crystals were obtained by the vapour-diffusion method in hanging drops. The crystals belong to the trigonal space group P3(1)21 or its enantiomorph P3(2)21, with unit-cell parameters a = b = 53.74, c = 67.45 A, alpha = beta = 90, gamma = 120 degrees. They diffract to at least 1.75 A. A selenomethionine derivative of the protein was prepared and crystallized for multiwavelength anomalous diffraction (MAD) phasing.