The efficacy of a pre-bone marrow transplantation (BMT) preparative regimen consisting of single, high dose rate total body irradiation followed by 12 courses of high dose cytosine arabinoside (Ara-C) over 6 days with allogeneic or autologous rescue was studied in 68 consecutive patients with poor risk acute lymphocytic leukemia (ALL). Toxicity associated with the above preparative regimen included conjunctivitis in the majority of patients, severe gastrointestinal symptoms in seven patients (10%), skin desquamation in four patients (6%), and interstitial pneumonitis of unknown etiology in two patients (3%). One patient died from a 'capillary leak' syndrome that may have been attributable to Ara-C toxicity. With a follow-up of 1.1-4.3 years, the estimated survival is 21% (95% confidence interval, 10-32%), with a disease-free survival of 18% (8-28%) and an estimated relapse rate of 75% (62-88%) at 3 years. These results are not significantly different from overall outcome in 105 patients treated previously at this same institution with cyclophosphamide-containing preparative regimens (31% (22-40%) estimated survival, 29% (20-38%) disease-free survival, and an estimated relapse rate of 63% (52-74%) at 3 years), especially when results are stratified based on allogeneic versus autologous BMTs. Although efficacious for a minority of patients with poor risk ALL, a pre-BMT preparative regimen consisting of total body irradiation followed by high doses of Ara-C did not improve long-term survival over more conventional preparative regimens consisting of cyclophosphamide and total body irradiation. Future strategies may need to investigate novel approaches for reducing leukemic relapse rates in patients with ALL undergoing bone marrow transplantation.