Crystals of the extracellular fragment of FcalphaRI/CD89 have been grown at 291 K using PEG 8000 as precipitant. The diffraction pattern of the selenomethionine (SeMet) derivative crystal extended to 2.1 A resolution at SPring-8, Japan. The crystals belong to space group C222(1), with unit-cell parameters a = 59.0, b = 69.4, c = 106.3 A, alpha = beta = gamma = 90 degrees. The presence of one molecule per asymmetric unit gives a crystal volume per protein mass (V(M)) of 3.12 A(3) Da(-1) and a solvent content of 60.2% by volume. A full set of X-ray diffraction data were collected to 2.1 A from an SeMet-derivative crystal.