Cyclic voltammetry was used to investigate the electrochemical behavior of prothrombin (blood coagulation Factor II) and thrombin, its product in the blood coagulation sequence. The results show that these proteins undergo adsorption and charge transfer reactions at the platinum electrode‐sodium chloride solution interface. The electrochemical conversion of prothrombin to thrombin at constant anodic potentials was attempted. Preliminary results indicate the possibility of intermediate electrochemical steps in the over‐all blood coagulation reaction.