Sixteen patients with poor-prognosis acute myelogenous leukemia (AML), acute lymphoblastic leukemia (ALL), and non-Hodgkin's lymphoma (NHL) underwent conditioning with busulfan (16 mg/kg) and cyclophosphamide (120 mg/kg) (BUCY-2) plus melphalan (90 or 135 mg/m2) and autologous bone marrow transplantation (AuBMT) in a phase I study. At the melphalan dose of 90 mg/m2, grade greater than or equal to 3 regimen-related toxicity (RRT) was observed in five patients (31%; 95% confidence interval [CI], 11% to 59%), with hepatic (venoocclusive disease [VOD]) and urinary (hemorrhagic cystitis) RRT being the most frequent complications. Further escalation of the melphalan dose to 135 mg/m2 was deemed excessively toxic, as three of five patients had grade greater than or equal to 3 RRT. Following this experience, 21 patients with multiple myeloma (MM) and chronic myelogenous leukemia (CML) were treated with BUCY-2 plus melphalan 90 mg/m2 and AuBMT in separate studies. Three of these patients--all with extensively pretreated MM--had grade greater than or equal to 3 RRT (14%; 95% CI, 3% to 36%); no others had grade greater than or equal to 3 RRT. Therefore, a total of eight of the 37 patients (22%; 95% CI, 10% to 38%) who received BUCY-2 plus melphalan 90 mg/m2 conditioning developed grade greater than or equal to 3 RRT; three of these patients (8%; 95% CI, 3% to 25%) died of RRT. Although limited by the relatively small number of patients, our analysis of the patients receiving this regimen showed that the presence of parameters denoting the lymphoid diagnostic group (ie, ALL, NHL, and MM), more extensive pretreatment, and/or more advanced disease status were associated with a higher incidence of grade greater than or equal to 3 RRT. Response data on the AML, ALL, and NHL patients who received BUCY-2 plus melphalan 90 mg/m2 were analyzed: three patients (all with AML in first or second remission) are leukemia-free at 3.0, 2.8, and 1.4 years after AuBMT. The actuarial 2-year event-free survival in this group is 17% (95% CI, 5% to 54%). Response data on the MM and CML patients will be reported subsequently. BUCY-2 plus melphalan at a dose of 90 mg/m2 before AuBMT produces acceptable toxicity in patients who are not heavily pretreated. A full evaluation of the antineoplastic effects of this regimen requires further study.