OBJECTIVES: I. Assess the feasibility and outcome of intensified induction/consolidation followed by intensified re-induction/re-intensification in infants less than 1 year of age with newly diagnosed acute lymphocytic leukemia (ALL). II. Evaluate the feasibility and outcome of bone marrow transplantation using family or unrelated donors in infants with the 11q23 abnormality. III. Evaluate neuropsychologic outcome upon completion of protocol therapy in patients who have reached the ages of 3 and 7 years, with special attention to the outcome in infants who received total-body irradiation. IV. Study the biology of infant ALL in samples of leukemic blood and bone marrow. V. Study the possible associations among patient- and disease-specific factors and family sociodemographic characteristics that mediate treatment outcome.