RATIONALE: Monoclonal antibodies, such as rituximab, can block cancer growth in different ways. Some find cancer cells and kill them or carry cancer-killing substances to them. Others interfere with the ability of cancer cells to grow and spread. Giving rituximab before chemotherapy may be an effective treatment for B-cell non-Hodgkin's lymphoma or B-cell acute lymphoblastic leukemia.

PURPOSE: This phase II trial is studying how well rituximab works in treating young patients who are planning to receive chemotherapy for B-cell non-Hodgkin's lymphoma or B-cell acute lymphoblastic leukemia.

OBJECTIVES:

• Determine the response rate in children and adolescents with B-cell non-Hodgkin's lymphoma (B-NHL) or B-cell acute lymphoblastic leukemia (B-ALL) treated with rituximab monotherapy as upfront window therapy before chemotherapy.
• Evaluate the effect of rituximab on different histological subtypes of childhood mature B-NHL or B-ALL in patients treated with this regimen.
• Investigate the rituximab response in patients treated with this regimen.
• Determine the toxicity profile of rituximab in these patients.
• Collect pharmacokinetic and pharmacodynamic data from patients treated with this regimen.

OUTLINE: This is a multicenter study.

Patients receive rituximab IV on day 1.

PROJECTED ACCRUAL: A total of 79 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Histologically and immunohistochemically OR cytomorphologically and immunphenotypically confirmed mature B-cell non-Hodgkin's lymphoma or B-cell acute lymphoblastic leukemia
• CD20 positive disease

PATIENT CHARACTERISTICS:

• Not pregnant or nursing
• Fertile patients must use effective contraception
• Adequate general condition with sufficient organ function (hepatic, renal, and cardiac)
• No known disease that would preclude protocol therapy with rituximab
• No known allergies against proteins
• No acute or previous hepatitis B infection

PRIOR CONCURRENT THERAPY:

• At least 2 weeks since prior corticosteroids
• No prior radiotherapy
• No prior or concurrent chemotherapy
• No concurrent treatment in another investigational trial