DISEASE CHARACTERISTICS: Histologically confirmed malignant solid tumor for which there are no therapeutic options that are potentially curative or have been demonstrated to increase survival No primary or metastatic CNS malignancy

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 70-100% Life expectancy: At least 12 weeks Hematopoietic: Neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9.0 g/dL Hepatic: Bilirubin normal SGOT no greater than 2.5 times upper limit of normal Renal: Creatinine normal OR Creatinine clearance at least 60 mL/min Cardiovascular: No atrial or ventricular arrhythmia requiring medication No ischemic event within the past 6 months Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No active infection No other active malignancy except curatively treated carcinoma in situ of the cervix or basal cell skin cancer No other serious concurrent medical illness No history of seizure disorder requiring active therapy

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks for mitomycin or nitrosoureas) and recovered Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy to more than 10% of bone marrow No prior electron-beam radiotherapy At least 4 weeks since other prior radiotherapy Surgery: Prior surgery allowed Other: Recovered from prior therapy