An electrochemical immunosensor for diagnosis of Forest-Spring encephalitis has been proposed. It comprises a screen-printed thick-film graphite electrode serving as the transducer and a layer of the Forest-Spring encephalitis antigen immobilized on the electrode and functioning as the biorecognition substance. The procedure includes formation of an antigen-antibody immune complex, localization of colloidal gold-labeled protein A on the complex, and recording of gold oxidation voltammogram, which provides information about the presence and the concentration of antibodies in blood serum. The response is proportional to the concentration of antibodies over the interval from 10(-7) to 10(-2) mg mL(-1). The detection limit is 10(-7) mg mL(-1).