Abstract Zone electrophoresis of histones in polyacrylamide gels provides resolution of components which is superior to that obtained with starch gels, and the reproducibility of the method is excellent. The method has been applied to a comparison of unfractionated calf thymus histones with various fractions obtained by the methods of Ui and Johns and Butler. The very lysine-rich histone fraction yielded 1 mobile band in starch gel and 9 bands in polyacrylamide gel. Crystalline pancreatic RNase yielded 2 major and 6 minor bands on electrophoresis in polyacrylamide gel, and the mobilities were comparable to those of some of the histone components. A method is described for estimation of relative amounts of electrophoretically separated components by determination of bound dye.