Twenty-two patients with early gastric cancer received injections of activated carbon particles (CH-40) to identify during surgery the location of non-palpable tumours present in the upper portion of the stomach. A few days before surgery, 0.2 ml of CH-40 was injected endoscopically into the gastric muscle adjacent to the cancer. In 20 of the 22 patients, the CH-40-stained area was recognized as a blackened patch on the serosal surface of the stomach which indicated the location of the non-palpable cancer tissue. The surgical margin for gastrectomy was defined as the proximal margin of the carbon-stained area and gastrectomies were performed on the 22 patients. CH-40 injection made it possible to choose the extent of lymph node dissection.