The globular domain of histone H1/H5 binds to the nucleosome and is crucial for the formation of chromatin higher order structure. We have expressed in Escherichia coli a gene that codes for the globular domain of H5. The protein produced in E. coli is functional in nucleosome binding assays. We have obtained crystals of the protein that diffract to beyond 2.5 A (1 A = 0.1 nm) resolution. The crystals are orthorhombic with unit cell dimensions of a = 80.1 A, b = 67.5 A and c = 38.0 A.