Extracorporeal devices for ultraviolet blood irradiation produce a therapeutical effect, but ensure no uniform irradiation of blood passing through a cuvette. They need a special procedure for cuvette sterilization. The intercorporeal devices simply the procedure of irradiation and require no use of anticoagulants. It is shown that they do not provide formed blood elements with the radiation energy required for their therapeutic effect. An extracorporeal device for blood irradiation with a disposal blood flow system that ensures uniform irradiation of the blood passing through the cuvette is described.