Possibility was investigated to prepare polysomes from microsomal fraction of rat sceletal muscles. Centrifugation in sucrose gradient showed that approximately 60 percent of UV-absorbing material in the preparation obtained was in polysomic region of the gradient. Mild treatment with pancreatic ribonuclease led to disintegration of polysomes and respective increase in content of monosomic component. The use of combined gradient permitted to obtain two fractions of polysomes, one of which was readily sedimented by centrifugation. This fraction contained significant amount of protein and incorporated relatively low quantity of 32-P within 2 hrs after administration of the label in vivo. The data obtained suggest that the fraction of polysomes carried out the biosynthesis of myosin.