EcoR124I is a multicomplex enzyme belonging to the type I restriction-modification system from Escherichia coli. Although EcoR124I has been extensively characterized biochemically, there is no direct structural information available about particular subunits. HsdR is a motor subunit that is responsible for ATP hydrolysis, DNA translocation and cleavage of the DNA substrate recognized by the complex. Recombinant HsdR subunit was crystallized using the sitting-drop vapour-diffusion method. Crystals belong to the primitive monoclinic space group, with unit-cell parameters a = 85.75, b = 124.71, c = 128.37 A, beta = 108.14 degrees. Native data were collected to 2.6 A resolution at the X12 beamline of EMBL Hamburg.