A procedure is proposed for electrophoretic studies of skeletal and smooth muscle myosins in 2.2% polyacrylamide gel at high ionic strength (mu = 0.4). When separated by electrophoresis myosin is shown to retain the ATPase activity which was dtermined histochemically directly in the gels. It is established that myosin molecules of the studied types of muscles have different electrophoretic mobility. At the electrophoresis on dodecylsulphate gels two types of light chains were detected in the smooth muscle myosin (their molecular weights being 26,900 and 17,800) in contrast to skeletal myosin which has three types of light chains. The obtained data evidence for existence of isoenzymic forms for myosin.