Veno-occlusive disease (VOD) of the liver is a major complication of bone marrow transplantation (BMT). The overall frequency of VOD has ranged from 20 to 30%, with a mortality rate greater than 40%, as reported by centers utilizing cyclophosphamide (Cy) and total body irradiation (CyTBI) or various chemotherapeutic regimens, including the busulfan (Bu) (4 mg/kg for 4 days) and Cy (50 mg/kg for 4 days) (BuCy4) combination. Since 1986, Hahnemann University (HU) has primarily used the BuCy2 regimen, i.e., Bu (4 mg/kg for 4 days) followed by Cy (60 mg/kg for 2 days). We reviewed 74 consecutive patients who received either an autologous or allogeneic BMT for various malignancies from January 1986 through October 1988 to determine the frequency of VOD. Seven of 74 consecutive patients met clinical criteria for VOD, for a total frequency of 9.5%. Fifty-five patients were conditioned with various other regimens. Only 5 of the patients conditioned with BuCy2 developed VOD (9.1%). This is less than the 25% reported frequency of VOD in patients who received CyTBI (1,000 rads) and less than the 24% reported frequency of VOD in patients who received BuCy4. Only one of seven patients who developed VOD died from the disease. One patient died of sepsis after the VOD had almost completely resolved. The remaining five completely recovered. We conclude that the total Cy dose, and not Bu, is the major factor in the occurrence of VOD in Bu/Cy BMT preparative regimens, and the BuCy2 regimen reduces the frequency of VOD in autologous and allogeneic graft recipients when compared to CyTBI or the BuCy4 regimens.