Assuming that cells and portions of tumor may remain in the abdominal cavity after surgery to reduce tumor size in cases of ovarian carcinoma, and that a change in cell kinetics could result in accelerated growth in the event of a recurrence, 23 patients with advanced tumors were given local (intraperitoneal) treatment intraoperatively. The treatment consisted of 15 mg Mitomycin C or 30 or 40 mg of Mitoxantron, in 1000 ml normal saline. Since the observation time was so short, the tolerance and side effects of this form of treatment were of primary interest, rather than remission quotas and survival times. The principal abdominal complaints included two subileus conditions which responded well to therapy and the problem of postoperative nausea. Four patients reacted to the treatment described with temperatures of over 38 degrees C. Chemical changes detected in the laboratory included 18 cases of leukopenia, which in one case reached WHO Grade 4. Intermittent changes in liver values and electrolytes were observed in isolated cases. Wound-healing impairments occurred in three cases. In one of them, a patient who sustained a prolapse of the small intestine with tumor growth into the abdominal wall, reoperation was necessary. Taken overall, the side effects of the intraoperative, intraperitoneal cytostatic therapy were acceptable. In view of the courses observed and with the idea of employing a form of therapy to combat aggressive growth of tumor cells remaining after surgery, it appears justified to continue with this form of treatment.