-INCLUSION CRITERIA:

          1. Diagnosis of CLL/SLL which is made according to the updated criteria of the NCI
             Working Group16.

          2. Active disease as defined by at least one of the following (iwCLL consensus criteria):

               -  Weight loss greater than or equal to 10% within the previous 6 months

               -  Extreme fatigue

               -  Fevers of greater than 100.5 F for greater than or equal to 2 weeks without
                  evidence of infection

               -  Night sweats for more than one month without evidence of infection

               -  Evidence of progressive marrow failure as manifested by the development of, or
                  worsening of

                    -  Anemia and/or thrombocytopenia

                    -  Massive or progressive splenomegaly

                    -  Massive nodes or clusters or progressive lymphadenopathy

                    -  Progressive lymphocytosis with an increase of >50% over a 2-month period, or
                       an anticipated doubling time of less than 6 months

          3. Must have designated hematologist/oncologist will assume care and provide venetoclax
             after the ramp-up phase is complete

          4. Must have G6PD testing performed to determine whether rasburicase can be given

          5. Must have HLA-testing performed to determine whether allopurinol hypersensitivity
             exists

          6. Age greater than or equal to 18 years

          7. ECOG 0-2

          8. Agreement to use acceptable methods of contraception for the duration of venetoclax
             treatment if sexually active and able to bear or beget children

          9. Willing and able to participate in all required evaluations and procedures in this
             study protocol including swallowing capsules without difficulty

         10. Able to comprehend the investigational nature of the protocol and provide informed
             consent

        EXCLUSION CRITERIA:

          1. Female patients who are currently pregnant or nursing

          2. Any uncontrolled active systemic infection

          3. Any life-threatening illness, medical condition, or organ system dysfunction that, in
             the investigator s opinion, could compromise the subject s safety or put the study
             outcomes at undue risk

          4. Known additional malignancy that is progressing or requires active treatment.

             --Note: Exceptions include basal cell carcinoma of skin, squamous cell carcinoma of
             skin, and in situ cervical cancer that has undergone potentially curative therapy.
             Further exceptions include other cancers from which the subject has been diseasefree
             for > 2 years, cancers which will not limit survival to < 2 years or cancers in
             remission receiving endocrine therapy.

          5. Richter s Transformation

          6. Any prior therapy with BCL-2 inhibitors

          7. Concomitant use of strong CYP3A4 inhibitors

          8. Disease significantly affecting gastrointestinal function or absorption

          9. Uncontrolled autoimmune hemolytic anemia or autoimmune thrombocytopenia

         10. Concomitant systemic cancer directed therapy (e.g. immunotherapy, chemotherapy,
             radiotherapy)

         11. Absolute neutrophil count (ANC) <1000/microL, platelets (Plt) <30,000/ microL

         12. Serum bilirubin >3 times upper limit of normal (ULN)

         13. Severe psychiatric illness/social situations or cognitive impairment that would limit
             the patient s ability to tolerate and/or comply with study requirements

               -  If the PI assesses the decreased ANC and/or Plt to be related to CLL involvement,
                  patients may still be enrolled in the study, as cytopenias as expected to improve
                  with treatment of CLL. Patients may receive supportive measures (e.g.
                  transfusions, IVIG, growth factor support, etc.) to avoid severe cytopenias prior
                  to and during therapy with venetoclax.