Thirty-four patients with advanced gastric cancers had received continuous hyperthermic peritoneal perfusion (CHPP) for prevention or treatment of peritoneal dissemination (PD). These patients received intra-abdominal perfusion 30-40 minutes by about 10-liter saline heated to 50-52 degrees C dissolving 200-300 mg cisplatin (CDDP) and 20-30 mg mitomycin C (MMC). The perfusate was infused in the peritoneal cavity through the peritoneal cavity expander (PCE Nihon Kayaku Co. Ltd.) newly developed for sufficient irrigation in our clinic. Eleven patients with macroscopic serosal invasion without PD (P0) or with mild PD (P1) underwent prophylactic CHPP for prevention of peritoneal recurrence. (Pn means degree of PD according to The General Rules for the Gastric Cancer Study.) Twenty-three patients with moderate PD (P2) or severe PD (P3) underwent therapeutic CHPP. The prognosis of patients having undergone prophylactic or therapeutic CHPP (CHPP (+) group) was compared with those not having done CHPP (CHPP (-) group) in the historical control study. In the prophylactic study two-year-survival rates of CHPP (+) group was 90% significantly higher than 63% in CHPP (-) group. There was no significant difference between two-year-survival rates of CHPP (+) (11%) and CHPP (-) (0%) in the therapeutic CHPP. But ascites was observed to disappear in five of twelve (41.7%). Surprisingly second look operation disclosed macroscopic and microscopic disappearance of PD in three of nine (33.3%). The side-effects in those patients had consisted of leakage, bone marrow suppression, perforation of small bowel and so on. But there was no mortality after introduction of PCE. About laboratory data, rises in WBC, BUN, creatinine and LDH and drops in total lymphocytes counts and platelets were all normalized within four weeks. The maximal concentrations of total and free, which emerged at five minutes after CHPP, were 2.19 and 1.29 micrograms/ml. These results suggested that CHPP with CDDP and MMC was well tolerated and effective for prevention of peritoneal recurrence and treatment of peritoneal dissemination in the gastric cancer.