To improve the results of high-dose therapy with autologous stem cell transplantation, new conditioning regimens with acceptable toxicity must be developed. The aim of this study was to evaluate the feasibility and toxicity of two myeloablative regimens performed at a 2-month interval. After salvage chemotherapy and collection of peripheral stem cell progenitors (median CD34+ cells/kg: 11 x 106/kg), (n = 15) patients with aggressive non-Hodgkin's lymphoma with poor prognostic factors or refractory Hodgkin's disease (n= 9) received intensified regimens. The first conditioning regimen, consisting of BCNU-cyclophosphamide-VP16-mitoxantrone was followed by transplantation of a median number of 4 x 10(6) CD34+ cells/kg; then, after a median interval of 56 days, a second preparative regimen, combining busulfan-aracytine-melphalan or TBI + aracytine-melphalan, was followed by transplantation of a median of 4 x 10(6) CD34+ cells/kg. After regimens 1 and 2, respectively: median time to neutrophil recovery >500/microl was 11 days (both times); median time to platelet counts >50,000/microl was 14 and 36 days, but values > 20,000/microl were reached by days 13 and 16 (P = 0.9); mucositis grade III-IV was observed in 11 and 15 cases. The median number of days with fever >38 degrees C was significantly higher (7.8 days) after the second transplant (P <0.05). Three cases of veno-occlusive disease (VOD) were observed after the second transplant. At a median follow-up of 18 months, 14/24 (58%) patients remained in CR, seven patients had died (two of VOD and five after relapse) and two were alive in relapse. These results indicate that tandem transplants performed at a 2-month interval in poor risk lymphoma can be used with acceptable hematotoxicity. VOD remains the major drawback and hepatotoxic drugs, such as busulfan, should be used with caution. Longer term follow-up of a larger cohort of patients is needed to ascertain the overall efficacy.