Crystals of monellin, a sweet protein from Dioscoreophyllum cumminsii , were grown by vapor diffusion of 20% ethanol into buffered protein solution. The crystals are orthorhombic, belonging to space group P2 1 2 1 2, with a = 54.4 Å, b = 113.0 Å, c = 40.8 Å, and V = 250,300 Å 3 . The asymmetric unit contains two complete molecules of monellin. The diffraction pattern of this crystal form extends to at least 2.5 Å, indicating that x-ray structural analysis is possible to near-atomic resolution.