The possibilities of fractionating histones and histone fractions by means of countercurrent distribution between two phases formed by water and butan-2-ol, in the presence of various concentrations of trichloroacetic acid, have been examined. 2. Although the principal histone fractions differ considerably in their partition ratios, a satisfactory resolution of the principal histone fractions from the whole histone has not been achieved. 3. The histone fractions obtained by other methods can be resolved with suitable concentrations of trichloroacetic acid. Besides the main peak several subsidiary peaks are obtained in most cases, the composition of which corresponds with others of the main fractions. 4. The method is therefore capable of removing from the principal fractions as previously prepared contamination by other fractions. 5. Except in one case, no fraction with composition unlike other fractions has been obtained. In several cases the material isolated from the principal peak behaves as a single component on running again. In two cases fractions with similar compositions were distinguished by countercurrent distribution.
