The processes by which Professor Setsuro Ebashi accomplished his great work are described. Independently of Marsh, Ebashi discovered the relaxing factor in homogenized muscle and showed that it has a lipid-containing particulate fraction with ATPase activity, later identified as the sarcoplasmic reticulum. He then solved the mechanism of relaxation of the relaxing factor through the following findings. A minute amount of calcium ion (Ca2+) is necessary for the physiological contractile reaction. The relaxing factor strongly accumulates Ca2+ in the presence of ATP and sufficiently removes Ca2+ from the contractile system to bring about relaxation. Ebashi found that the contractile reaction of myosin and actin is regulated by Ca2+ only in the presence of a tropomyosin-like protein factor, which he later showed to be a complex of tropomyosin and a new protein, troponin. He proved that troponin is the Ca2+-receptive protein and proposed the correct scheme for the molecular mechanism of regulation of contraction and relaxation. (c) 2008 Elsevier Inc. All rights reserved.