A 35-year-old man was treated for pseudomyxoma peritonei by surgery and by thermal infusion and chemotherapy with a machine designed specifically for the treatment of cancers of serosal surfaces. After extensive abdominal resection and closure, the patient's peritoneal cavity was instilled with 2.5 liters of 5% lactated Ringer's solution. He was then attached to hyperthermic perfusion system which elevated the i.p. temperature by warming (to 42 degrees) and recirculating the effusion solution. When the 42 degrees i.p. temperature was attained (after 1.5 hr), chemotherapy was added to the recirculating effusion. A second procedure followed 8 days later. The patient's postoperative course was uneventful except for minor pulmonary atelectasis with bacteremia. Hyperthermic perfusion was tolerated well and was evaluated as safe for intracavitary cancer treatment.