OUTLINE: This is a dose escalation study. Patients receive intravenous leucovorin calcium for 60 minutes and bolus infusions of fluorouracil (5-FU), followed by gemcitabine infusions, weekly for six weeks followed by 2 weeks of rest. The dosage of gemcitabine is increased if fewer than 3 of the first 6 patients experience grade 3-4 toxicities. Phase II proceeds at the maximum tolerated dose (1 dose level below that at which 3 patients experience grade 3-4 toxicities). Patients receive a minimum of two courses of treatment to be considered evaluable for response. Patients with stable disease, partial, or complete remission may continue therapy for up to six treatment cycles. Patients exhibiting disease progression or intolerable toxic effects are removed from the study.