Biochemical monitoring suggests that there is profound and sustained inhibition of DPD with a single dose of 20 mg PO 776C85 days 1-3 each week for three of four weeks. Once the MTD has been defined for the once daily dosing on days 1, 2, 3 schedule, a simplified schedule will be evaluated in which a single dose of 776C85 on day 1 in the evening, with oral leucovorin days 1 and 2, and 5-FU given day 2 as a single dose.