Three days after denervation of the gastrocnemius muscle of rabbits the histone DNA ratio increases 40% in muscle cell nuclei. Electrophoresis of the histones in starch gel showed that the increase is due to an increase in fraction F2al. After a tenotomy the proportion of the histone fractions remained the same as in an intact muscle. A theory is advanced concerning the possible regulatory effect of nerve impulsation on processes occurring at the level of nuclear structures.