1. Patients that are high risk for TLS or potential/intermediate risk for TLS as described below: (a) High risk: Hyperuricemia of malignancy (Uric acid levels >7.5); or diagnosis of very aggressive lymphoma/leukemia based on Revised European-American Lymphoma (REAL) classification; acute myeloid leukemia, CML in blast crisis; high grade myelodysplastic syndrome only if they have >10% bone marrow blast involvement and given aggressive treatment similar to acute myeloid leukemia (AML). (b) Potential risk: Diagnosis of aggressive lymphoma/leukemia based on (REAL) classification. Plus one or more of the following criteria: lactate dehydrogenase (LDH) >/= 2 x upper limit of normal (UNL); Stage III-IV disease; Stage I-II disease with at least 1 lymph node/tumor > 5 cm in diameter. For patients with potential/intermediate risk for TLS- Only those planned to receive alternating regimens (or non-standard regimens) in 2 cycles (example; R-Hyper-central venous access device (CVAD) alternating with MTX/ARA-C) will be eligible.