Eighteen patients with hepatic metastases primarily from colorectal carcinoma were treated on a phase I protocol employing hepatic artery infusion (HAI) of 5-fluorouracil (FUra) and 5-iodo-2'-deoxyuridine (IdUrd) via implantable infusion pump. Patients received a 14-day continuous HAI of 300 mg/day FUra. During days 8-14 of therapy, patients received IdUrd as a separate 3-h HAI daily x 7. Treatment cycles were repeated every 28 days. IdUrd was escalated from 0.1 to 2.86 mg/kg/day x 7. Myelosuppression and stomatitis were mild and not dose limiting. Hepatotoxicity was dose limiting and similar to that reported for 5-fluoro-2'deoxyuridine alone administered as a 14-day infusion every month. One patient developed a clinical picture consistent with sclerosing cholangitis and another had biopsy-proven cholestasis and triaditis. Catheter complications occurred in 7 of 18 patients. Plasma concentrations of FUra during the 7-day continuous HAI of FUra alone were consistently either undetectable or very low (less than or equal to 0.1 microM). At level 3 (1.0 mg/kg/day IdUrd) and beyond, measurable plasma concentrations of FUra, iodouracil, and IdUrd were found at the end of the daily 3-h infusion of IdUrd. The maximum tolerated dose of IdUrd as administered in this trial is 2.2 mg/kg/day x 7 and the recommended starting dose for further clinical investigation is 1.7 mg/kg/day x 7.