Perchloric acid soluble protein purified from the cytosol fraction of rat liver has been crystallized in a form suitable for high-resolution X-ray diffraction studies. Octahedral crystals reaching 0.5 mm in cross-sectional diameter were produced by the hanging-drop method using polyethylene glycol (Mr = 8 kDa) as precipitant. These crystals diffract to 2.44 A on an in-house X-ray source and to 1.8 A using a bending-magnet beamline at ESRF Grenoble. The crystals belong to the cubic space group P213 with a = 89.90 A and two molecules per asymmetric unit, as indicated from a Vm value of 2.12 A3 Da-1 and self-rotation function computation. Screening for heavy-atom derivatives identified a platinum compound and xenon that bind to the protein.