DISEASE CHARACTERISTICS: Histologically proven metastatic, refractory solid tumors for which no curative therapy exists No more than 2 prior chemotherapy regimens for metastatic disease No prior high dose chemotherapy regimen requiring bone marrow transplantation or peripheral blood stem cell transplantation No hematologic malignancies No brain or leptomeningeal disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Not specified Life expectancy: At least 12 weeks Hematopoietic: Absolute neutrophil count at least 2,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin normal (no greater than 1.5 times upper limit of normal (ULN) if liver metastases present) SGOT and SGPT normal (no greater than 5 times ULN if liver metastases present) Hepatitis B negative Renal: Creatinine less than 1.5 mg/dL EDTA clearance greater than 60 mL/min Other: Not pregnant or nursing Fertile patients must use effective contraception during and for 6 months after study No severe concurrent nonmalignant disease that would preclude protocol therapy HIV negative No AIDS related illness No mental incapacity

PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics At least 4 weeks since prior immunotherapy and recovered No concurrent biological response modifier therapy or immunotherapy No concurrent prophylactic growth factors Chemotherapy: See Disease Characteristics No prior camptothecins (e.g., irinotecan or topotecan) At least 4 weeks since other prior chemotherapy (6 weeks for nitrosoureas and mitomycin) and recovered No other concurrent chemotherapy Endocrine therapy: At least 4 weeks since prior hormonal therapy and recovered No concurrent corticosteroids used as anticancer therapy No other concurrent hormonal therapy Radiotherapy: No prior radiotherapy to greater than 25% of bone marrow At least 4 weeks since other prior radiotherapy and recovered No concurrent radiotherapy Surgery: Not specified Other: No concurrent investigational drug or participation in other clinical study