Inclusion Criteria:

- Pathologically confirmed acute myeloid leukemia or acute lymphoblastic leukemia:

- Relapsed >= 1 time OR refractory disease:

- Patients who fail primary induction therapy or who relapse after achieving
complete remission are eligible if they have received =< 3 prior courses of
induction/reinduction therapy

- Relapsed >= 1 time OR refractory disease

- Patients who fail primary induction therapy or who relapse after achieving complete
remission are eligible if they have received =< 3 prior courses of
induction/reinduction therapy

- No active CNS leukemia

- ECOG performance status 0-2

- AST and ALT =< 5 times upper limit normal (ULN)

- Alkaline phosphatase =< 5 times ULN

- Bilirubin =< 2.0 mg/dL

- Creatinine =< 2.0 mg/dL

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- LVEF >= 45% by MUGA or ECHO

- No active, uncontrolled infection

- No other life-threatening illness

- No mental deficits and/or psychiatric history that would preclude study compliance

- No active graft-vs-host disease

- Recovered from all prior therapies

- At least 24 hours since prior hydroxyurea, steroids, imatinib mesylate, arsenic
trioxide, interferon, or leukapheresis for blast count control

- At least 4 weeks since prior stem cell transplantation (autologous or allogeneic)

- At least 4 days since prior growth factors

- At least 3 weeks since prior chemotherapy, except for non-aplasia producing
treatments (e.g., low-dose cyclophosphamide, hydroxyurea, interferon, imatinib
mesylate, mercaptopurine, thalidomide, azacitidine, or decitabine)

- No prior flavopiridol

- No other concurrent chemotherapy, radiotherapy, or immunotherapy

- No acute promyelocytic leukemia (M3)

- No hyperleukocytosis with > 50,000 blasts/mm^3