Endoscopic photodynamic therapy (PDT) using a pulsed gold vapor laser (wavelength 628 nm, LaserSonics Inc.) was performed on eight cases of early gastric cancer. Three patients refused to have surgery, and the others were in a high-risk group due to old age or complications with other diseases. Hematoporphyrin derivative (HpD I, 2.5-3 mg/kg, Photofrin Inc.) was injected intravenously, and 48-72 hours later, the entire cancer lesion and 5 mm width mucosa encircling it were irradiated with a gold vapor laser through a single quartz fiber. The irradiation was delivered at 300-330 mW for 5-20 minutes, which gave about 90 J/cm 2 dosage. In seven of eight cases, local cure was achieved. Recurrence was noted only in one patient. In one of eight patients, operation was carried out 1 month after PDT. Pathological examination of the resected stomach revealed that the effect of PDT extended into the tunica muscularis propria. Side effects of HpD, such as skin rash, were noted in two patients, but no serious complications of PDT were encountered. This suggests that PDT with a pulsed gold vapor laser is clinically useful in the treatment of early gastric cancer.