Based on encouraging results of a recently published study on the clinical usefulness of oral pentoxifylline (PTX) to reduce transplant-related toxicities, prophylactic pentoxifylline was administered to 31 consecutive allogeneic BMT recipients with hematological malignancies. Patients received PTX as a continuous infusion at increasing dose levels (0.50, 0.75, 1.00 and 1.25 mg/kg/h) starting 1 day prior to the conditioning regimen. At all dose levels, PTX was well tolerated with no significant side-effects. When compared with a historical control group of 61 consecutively transplanted allogeneic BMT recipients, PTX patients did not appear to experience less gastrointestinal (moderate and severe mucositis: 100% vs 68%, p < 0.001), hepatic (hyperbilirubinemia > 1.5 mg/dl: 84% vs 30%, p < 0.001) or renal (creatinine > 1.5 mg/dl: 16% vs 27%, NS) toxicity or to have a lower incidence of GVHD > or = grade III (21% vs 22%, NS). Using i.v. PTX, we were unable to reproduce the reduction in morbidity and mortality in patients undergoing BMT which has been described for prophylactic oral PTX.