The adsorption and charge transfer reactions of fibrinogen, one of the blood coagulation factors, have been investigated using ellipsometric, potentiodynamic, and steady‐state potentiostatic methods. The protein is adsorbed on platinum over a wide potential range (−600 to +800 mV vs. SCE) even at very low concentrations. Steady‐state potentiostatic studies show that it is involved in anodic and cathodic charge transfer reactions. Adsorption plays a prominent role in the development of potentiokinetic peaks and in their shifts with scan rate variation. The observed charge transfer reactions of this protein throw new light on the correlations between blood compatibility of metallic materials and their spontaneous potentials in blood.