An unfocused continuous-wave carbon dioxide (CO2) laser was used in dogs with bleeding gastric ulcers or erosions. The laser radiation was delivered through an endoscope introduced orally. In seven dogs, anesthetized and heparinized, bleeding ulcers caused by hot acid jets stopped after five seconds of laser radiation. In four additional dogs, similar ulcers required five minutes of electrocoagulation for hemostasis. In seven dogs, bleeding from mechanically caused abrasions was stopped in three to five seconds by laser. In five other dogs, such abrasions required five minutes of coagulation. Laser radiation produced a thin coagulum on the surface of the lesions. Regenerating mucosa was seen in all dogs at killing after seven days. The rapid production of hemostasis leads to consideration of the CO2 laser in certain poor-risk patients who have massive bleeding from gastric erosions.