A seed globulin from Vicia narbonensis L. has been crystallized by vapour diffusion induced pH-shift. Crystals are suitable for high-resolution X-ray structural analysis and diffract to better than 1.5 A. Narbonin crystallizes in the monoclinic space group P21 with alpha = 46.9 A, b = 75.5 A, c = 50.9 A, alpha = gamma = 90 degrees, beta = 120.5 degrees. The protein consists of one polypeptide chain that does not coincide with the subunits of legumin or vicilin after SDS/polyacrylamide gel electrophoresis and has a relative molecular mass of about 33,000.