Antibodies were raised to myosins extracted from the cytoplasm and solubilized membranes of human blood platelets. Both antibodies had similar titers as shown by enzyme-immunoassay and bound to the same sites as shown by immunohistochemistry. They were specific for cytoplasmic myosins (e.g., in human white blood cells, platelets and fibroblasts and rat endothelial cells). They showed no crossreaction with human or rat smooth muscle.