DISEASE CHARACTERISTICS: Histologically confirmed malignancy that is metastatic to the CSF or leptomeningeal/subarachnoid space, including the following: Leukemia Lymphoma Germ cell tumors Persistent or recurrent disease required Cytologic evidence of malignancy in CSF or evidence of leptomeningeal tumor by CT or MRI No obstructive hydrocephalus or complete block of spinal CSF pathways on pre- study MRI or CT No rapidly progressing or deteriorating neurological deficit

PATIENT CHARACTERISTICS: Age: 3 and over Performance status: Karnofsky 60-100% (age 10 and over) OR Lansky 60-100% (age under 10) Life expectancy: At least 8 weeks Hematopoietic: Absolute neutrophil count greater than 1,000/mm3* Platelet count greater than 100,000/mm3* * Lower values allowed with approval of the investigator Hepatic: Bilirubin less than 3.0 mg/dL Renal: Creatinine less than 2 mg/dL Blood urea nitrogen less than 30 mg/dL Electrolytes (including calcium, magnesium, phosphate) normal Other: No active infection Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Prior systemic chemotherapy within 3 weeks of entry allowed at investigator's discretion At least 3 weeks since prior intrathecal chemotherapy No other concurrent intrathecal chemotherapy Endocrine therapy: Not specified Radiotherapy: At least 3 weeks since prior radiotherapy to the CNS No concurrent radiotherapy to the CNS Surgery: Not specified