INTRODUCTIONCore histones can be purified from a variety of cell sources, including Drosophila embryos, HeLa tissue culture cells, calf thymus, or chicken erythrocytes. Chick erythrocytes are an excellent source of cellular histones: Large quantities of source material are readily obtainable, the purified histones have low levels of post-translational modifications, and linker histones can also be purified from the same cell sample. Also, avian histones have an amino acid sequence identical to that of human histones. Histone stocks can be stored successfully for more than a year at 4°C and for several years at −20°C. With this protocol, 200 mL of blood usually yields in excess of 50 mg of purified histone octamers. Additional optional procedures are also presented for the purification of H1 and H5 linker histones, as well as for the preparation of H3/H4 tetramers and H2A/H2B dimers.