Phase I clinical and pharmacologic study of intraperitoneal cisplatin and fluorouracil in patients with advanced intraabdominal cancer. Fluorouracil (5-FU) and cisplatin display marked therapeutic synergy in preclinical models and are effective in the treatment of a number of solid tumors when combined and administered intravenously (IV). Each drug has also been administered intraperitoneally (IP) and displays a favorable pharmacologic profile and acceptable clinical toxicity. We therefore undertook a phase I study to determine the feasibility and toxicity of combination IP chemotherapy with these agents. Thirty-one patients with histologically documented malignancy confined to the peritoneal space were treated with cisplatin 90 mg/m2 mixed with 5-FU in 2 L of lactated Ringer's solution and given IP for 4 hours every 28 days. Cohorts of at least three patients received starting 5-FU concentrations ranging from 5 mmol/L (1,300 mg in 2 L) to 20 mmol/L. The dose-limiting toxicity was neutropenia with a median granulocyte nadir of 156 cells per microliter occurring at a 5-FU dose of 20 mmol/L. Intrapatient escalation of the 5-FU dose was permitted and 15 cycles of chemotherapy were delivered at 5-FU concentrations greater than 20 mmol/L, the highest concentration being 30.7 mmol/L (8 g of 5-FU in 2L). Other toxicities included mild to moderate nausea during all cycles of therapy, vomiting in 54% of cycles, and diarrhea in 15% of cycles. Abdominal pain, renal dysfunction, peripheral neuropathy, and oral mucositis occurred infrequently and were not related to the 5-FU dose. Peritoneal fluid and plasma 5-FU concentrations were measured by high-performance liquid chromatography (HPLC) in selected patients. Mean peak plasma 5-FU concentrations ranged from 6.19 mumol/L to greater than 60 mumol/L, and peritoneal fluid to plasma 5-FU area under the curve (AUC) ratios ranged from 85 to 1,150. Nine of 15 patients with nonbulky disease had resolution of malignant ascites or at least a 50% reduction of peritoneal studding by tumor at repeat laparotomy. We conclude that combination IP chemotherapy with cisplatin and 5-FU is technically feasible and has acceptable clinical toxicity and a favorable pharmacologic profile. The recommended starting 5-FU dose for phase II trials is 3,900 mg mixed with 90 mg/m2 of cisplatin in 2 L of isotonic fluid. 