In contrast to the earlier reports on the age-dependent reduction of the ratio of F3 plus F2al plus F2a2 / Fl plus F2b in rat liver histones and the reduction of arginine-rich histone (F3 or III) in beef thymus, the result obtained by high-resolution polyacrylamide gel electrophoresis of histones shows no apparent age-related change in the proportion of any histone fraction of mouse and rat liver chromatin.