A recombinant form of Arthrobacter globiformis inulin fructotransferase (DFAIII-producing) has been overexpressed in Escherichia coli and purified to homogeneity. Crystals were obtained at 293 K by the hanging-drop vapour-diffusion technique using 0.1 M Na HEPES pH 7.5 buffer containing 1.5 M lithium sulfate as a precipitant. Crystals of the recombinant wild-type enzyme diffracted to better than 1.5 A at 100 K using a synchrotron-radiation source at the Photon Factory. The crystal belonged to space group R32, with unit-cell parameters a = b = 92.02, c = 229.82 A in the hexagonal axes. Assuming the presence of one molecule in the asymmetric unit, the V(M) value for the crystal was 2.15 A(3) Da(-1), indicating a solvent content of 42.8%. Selenomethionine-derivative crystals belonged to a different space group, C2, with unit-cell parameters a = 159.32, b = 91.92, c = 92.58 A, beta = 125.06. Matthews coefficient calculations suggested that the C2 selenomethionine-derivative crystal contained three molecules per asymmetric unit.