After a 2 week rest period and resolution of any toxicities experienced during the first period of treatment, patients are given an escalating dose of fluorouracil with fixed doses of leucovorin calcium and ethynyluracil. Ethynyluracil and leucovorin calcium are given bid orally on days 1-3 of each week. Fluorouracil is given bid orally on day 2 of each week. Treatment is repeated for three weeks followed by a one week rest period.