OBJECTIVES: I. Evaluate the maximum tolerated dose (MTD) of continuous infusion topotecan in combination with fluorouracil for patients with advanced malignancy and establish a recommended phase II dose based on the MTD. II. Evaluate the dose limiting toxicity of this combination in these patients. II. Obtain pharmacokinetic and pharmacodynamic data for topoisomerase-1 depletion in patients receiving this treatment. IV. Identify any objective tumor responses arising from this treatment in these patients.