OBJECTIVES: I. Determine the safety, tolerability, maximum tolerated dose, and dose limiting toxicity of oral SCH 66336 with fluorouracil and leucovorin calcium in patients with advanced malignancy. II. Assess the multiple dose pharmacokinetics of oral SCH 66336 when administered with fluorouracil and leucovorin calcium. III. Assess the pharmacokinetics of fluorouracil when administered with oral SCH 66336. IV. Assess antitumor activity of oral SCH 66336 with fluorouracil and leucovorin calcium in these patients.