It is now well accepted that the light chains of myosin are an essential feature in the biological functioning of the molecule. It is proposed in the study 1) to elucidate further the nature of the interaction between light and heavy chains, 2) to investigate the properties of light chains from myosins of various sources, 3) to perform hybridization experiments between light and heavy chains of various myosins. It is hoped that these studies will provide insight into the role of the light chains in the mechanism of the interaction of myosin with ATP, Ca ions, Mg ions and F-actin.