Cohorts of 3-6 patients receive escalating doses of 5-FU until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that at which at least 2 of 3 or 2 of 6 patients experience dose-limiting toxicity. The recommended phase II dose (RPIID) is defined as the dose preceding the MTD. At least 6 additional patients are treated at the RPIID.