OBJECTIVES: I. Determine the safety profile, maximum tolerated dose, and dose limiting toxicities of PNU 166148 in patients with metastatic, refractory solid tumors. II. Define a recommended dose of PNU 166148 for a Phase II study. III. Determine the pharmacokinetic profile and molecular weight distribution of PNU 166148 and the pharmacokinetic profile of free camptothecin in these patients. IV. Assess any evidence of antitumor activity in these patients treated with this regimen.