RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die.

PURPOSE: Phase I trial to study the effectiveness of raltitrexed in treating children with refractory acute leukemia.

OBJECTIVES: I. Determine the maximum tolerated dose and dose limiting toxicity of raltitrexed given for three weeks to children with refractory acute leukemia. II. Determine the incidence and severity of other toxic effects of this regimen in these patients. III. Determine a safe and tolerable dose of raltitrexed, administered in this manner, to be used in phase II studies. IV. Determine the pharmacokinetics of this regimen in these patients. V. Determine if plasma 2' deoxyuridine concentrations are associated with raltitrexed toxicity or pharmacokinetics. VI. Evaluate the antitumor activity of raltitrexed against recurrent leukemia.

OUTLINE: This is a dose escalation study. Patients receive raltitrexed intravenously over 15 minutes once weekly for 3 weeks followed by 1 week of rest. Treatment continues in the absence of disease progression and unacceptable toxicity. In the absence of dose-limiting toxicity (DLT) in the first cohort of 6 patients treated, subsequent cohorts of 6 patients each receive escalating doses of raltitrexed on the same schedule. If DLT occurs in 2 of 6 patients at a given dose level, then dose escalation ceases and the next lower dose is declared the maximum tolerated dose. Patients are followed every 6 months for 4 years, then annually thereafter.

PROJECTED ACCRUAL: This study will accrue 8 patients per year, for a total of approximately 30 patients.

DISEASE CHARACTERISTICS: Histologically or cytologically proven acute leukemia (M3 marrow) that is refractory to conventional therapy or for which no effective therapy exists No CNS leukemia No solid tumors

PATIENT CHARACTERISTICS: Age: 21 and under Performance status: Karnofsky 50-100% OR Lansky at least 50 (for infants) Life expectancy: At least 8 weeks Hematopoietic: Not specified Hepatic: Bilirubin less than 1.5 mg/dL SGPT less than 5 times normal Renal: Normal creatinine for age OR GFR at least 70 mL/min Other: No significant systemic illness such as infection No significant third space fluid collections Not pregnant or nursing

PRIOR CONCURRENT THERAPY: Biologic therapy: Recovered from acute toxic effects of prior immunotherapy At least 6 months since prior bone marrow transplant with no evidence of graft-versus-host disease At least 10 days since prior biologic therapy At least 1 week since prior growth factors Chemotherapy: At least 2 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosourea) and recovered Endocrine therapy: No concurrent steroids Radiotherapy: Recovered from acute toxic effects of all prior radiotherapy At least 2 weeks since prior local palliative radiotherapy (small port) At least 6 months since prior substantial bone marrow radiation Surgery: Not specified Other: No other concurrent anticancer therapy or investigational agents No concurrent nonsteroidal anti-inflammatory agents