An unblinded, historical controlled study of 49 bone marrow transplant (BMT) patients was carried out in our institution to assess the effect of oral pentoxifylline (PTX) on BMT regimen related toxicity (RRT). Twenty-eight consecutively treated BMT patients (17 allogeneic, 11 autologous) were entered into the PTX treatment group and treated with oral PTX 400 mg at intervals of 4 h from day -10 until day +35 or discharge, whichever came sooner. These were compared with a control group of 21 BMT patients (14 allogeneic, 7 autologous). Patient groups were very similar with respect to age, sex, conditioning regimen, graft-versus-host disease (GVHD) prophylaxis and baseline liver and renal function. Compliance with the drug was 85%. Despite this, no significant difference in days of mucositis or hyperalimentation, incidence or severity of renal or hepatic dysfunction, hypertension, GVHD, weight gain > 5%, day 100 mortality or length of hospitalization was observed. Median follow-up is > 2 years in both groups and no difference in relapse or survival was observed. We were unable to confirm an effect of oral PTX on BMT related morbidity or mortality.