This study will evaluate the response rate to treatment with pentostatin in steroid-refractory acute graft versus host disease.

Inclusion Criteria:

• Must have biopsy proven grade II-IV acute GVHD refractory to systemic corticosteroids
• No chronic GVHD
• Age ≥ 18 years
• Evidence of myeloid engraftment (ANC ≥ 0.5 x 109/l)
• Performance status 0-3

Exclusion Criteria:

• Patients on mechanical ventilation or who have resting O2 saturation <90% by pulse-oximetry.
• Patients on renal dialysis or who have an estimated creatinine clearance of < 30 ml/min/1.73 m2.
• Patients with documented clinical infection (progressive symptoms despite antibiotics or continued fever) cannot be enrolled on study until infection is controlled.