Based on laboratory studies showing enhanced cytotoxicity of floxuridine (FUDR) when used with high doses of leucovorin (LV), a pilot study of FUDR and LV through an implantable pump was initiated for the treatment of hepatic metastases from colorectal cancer. The highest dose of LV that could be administered, taking into account the constraints of the capacity of the pump and the solubility of LV, was 120 mg/m2/d. Due to the possibility of added toxicity, 25% of this dose was initially used. Twenty-four patients were treated at three dose levels. Eight patients were treated with the combination of LV (30 mg/m2/d) and FUDR (0.3 mg/kg/d) for a 14-day infusion through the pump, alternating with 2 weeks of saline. All eight patients had a greater than 50% decrease in measurable disease (PR) and a greater than 50% decrease in carcinoembryonic antigen (CEA) value; however, sclerosing cholangitis developed in two of these patients within 4 months. The next seven patients were treated with a lower dose of FUDR (0.2 mg/kg/d) and the same dose of LV, both for 14 days. Four of seven patients had a PR, and toxicity was decreased with no biliary sclerosis. A third regimen explored the combination of FUDR (0.3 mg/kg/d) and LV (30 mg/m2/d) for 7 days, alternating with 1 week of saline, to evaluate a shorter interval of treatment with the same overall dose intensity. Six of nine patients had a PR and all patients had a greater than 50% decrease in CEA value; sclerosing cholangitis developed in three of these patients. The overall response rate was 72%, with 18 of 25 patients alive after 1 year. The median survival time has not been determined, but it is greater than 27 months. FUDR with LV appeared to be effective in the treatment of hepatic metastases from colorectal carcinoma, but hepatic toxicity appeared to be greater than that previously reported with FUDR alone.