Pharmacokinetic considerations and tests with cell lines and individual cell suspensions from metastatic human solid tumor biopsies suggested testing the efficacy of mitoxantrone (NOV) in intraperitoneal regional chemotherapy (IPRC). Twenty-seven patients with intraperitoneal metastatic disease of various solid tumors received cyclic IPRC with NOV for treatment of malignant ascites (N = 16) or of peritoneal carcinomatosis (N = 11) at a NOV instillate concentration of 10 micrograms/ml. A total of 125 cycles (1-5 per patient) were applied. Response and toxicity were registered according to WHO criteria. The response rate (CR+PR) was 56 percent in malignant ascites, 45 percent in peritoneal carcinomatosis, and 52 percent overall. There were no systemic toxicities. Regional side effects were bacteriemia (4 of 125 cycles), pain (2 of 125 cycles), small bowel stricture (1 of 27 patients), and small bowel perforation (1 of 27 patients). From these results we can conclude that NOV appears to be effective in IPRC for malignant ascites and peritoneal carcinomatosis at tolerable toxicities.