A sensitive spectrophotometric method for the determination of DNA binding protein, histone, is developed. The proposed method is based on color reaction among histone, 3,4,5,6-tetrafluoro-2-carboxyphenylfluorone (TFCPF) and manganese(II). The coloration obeys Beer's law in the concentration range of 1.0-20 mug cm(-3) histone. Other proteins such as human serum albumin and gamma-globulin are scarcely produced colored complexes. A detection test of histone on a spot plate was also studied.