Some basic principles of medical applications of lasers are considered. It is shown that a low-intensity radiation of a Cu-vapor laser at the wavelengths l = 510.6 nm and l = 578.2 nm can affect tumor processes. A comparative clinical data on the laser therapy effects of a He-Ne laser radiation and radiation of a Cu-vapor laser on the stomach ulcer are presented. Clinical data have been obtained from numerous observations. The best therapeutic effect has been observed in the case of patients with chronic callous ulcers.