We studied the pharmacokinetics of the intraperitoneal administration of CPT-11 for four patients with peritoneal metastasis (2 gastric cancer cases, 2 colon cancer cases). CPT-11 was administrated in a dose of 40-60 mg and the intraperitoneal and serum levels of CPT-11, SN-38 and SN-38 glucuronized (SN-38 Glu) were measured periodically. Intraperitoneal therapy with CPT-11 was effective for the control of malignant ascites. No serious side effects were observed. The levels of CPT-11, SN-38 were no different 30 min afterwards the administration of CPT-11 either intraperitoneally or intravenously. The high concentration of CPT-11 was achieved with intraperitoneal therapy and a small fraction of CPT-11 changed into SN-38 in the abdominal cavity.