Intra-peritoneal chemo-hyperthermia with mitomycin C was used to treat 9 patients with very advanced gastrointestinal cancers with peritoneal seedings. Resection of the primary tumor was possible in 3 cases. After temporary of closure of the abdominal wall, 90 to 120 minutes of intra-peritoneal chemo-hyperthermia was performed under general anaesthesia with 32 degrees C of systemic hypothermia, via 3 intra-peritoneal drains forming a closed circuit, using 10 mg/l of mitomycin C in 61 of peritoneal dialysate warmed at the inflow temperature of 46 to 49 degrees C. We observed no mortality or morbidity. There were only minor and temporary laboratory side effects and for 6 patients, no malignant cells could be found in the ascitic fluid after intra-peritoneal chemo-hyperthermia. In six patients, we conserved an improvement in the Karnofsky index 3 to 7 months after intra-peritoneal chemo-hyperthermia. These results show that intraperitoneal chemo-hyperthermia with mitomycin C is a safe and reliable treatment for peritoneal seedings in severely advanced gastrointestinal cancers and encourage us to proceed with this new therapeutic modality.