Fifteen patients with acute leukemia resistant to standard chemotherapy were treated by bone marrow transplantation from HLA-matched siblings after conditioning with a new combination chemotherapy/radiation therapy regimen--SCARI. SCARI consists of 5 days of high-dose cytosine arabinoside and 6-thioguanine followed by 3 days of daunorubicin. After a rest period, cyclophosphamide and total-body irradiation are given sequentially. This regimen had acceptable morbidity. Median survival was 169 days. Overall survival and disease-free survival was 27% at over 11 months. Relapse rate was 13% of the entire group and 30% by actuarial projection. Relapses were late and initially extramedullary. Deaths from causes other than leukemia occurred early secondary to fungal infection and late secondary to interstitial pneumonia (frequently cytomegalovirus). Graft-versus-host disease and graft rejection were not causes of mortality. In these patients conditioned with SCARI, leukemic recurrences were infrequent but infectious complications were a major hazard.