OBJECTIVE To evaluate the toxic extramedullary morbidity of the conditioning treatment with BuCy for BMT, as well as the usefulness of pentoxyphyllin (PTX) and methylprednisolone (MP) in the prophylaxis of mucositis. METHODS Forty-eight patients with blood malignancies (AML, 19; ALL, 14; indifferentiated AL, 1; CML, 9; lymphoblastic lymphoma, 3; RAEB, 1; RAEBT, 1), subjected to BMT (16 autologous and 32 allo-BMT) were retrospectively revised. They all had been treated with BuCy as conditioning regimen. The GVHD prophylaxis was made in allo-BMT with cyclosporin and short-term methotrexate. Twelve patients received PTX-MP as mucositis prophylaxis. RESULTS Some kind of toxicity was found in 47 of the 48 patients, mostly grade I-II (45 cases). The commonest sites involved were the mouth (87.5%) and the liver (30.23%). Neither veno-occlusive liver disease nor pulmonary toxicity were present in any case. Heart toxicity was seen only in 2 cases, while 3 had haemorrhagic cystitis due to Cy. The severity of the mucositis was lesser in those patients receiving PTX-MP, so the requirements of NPT were lower in them (p = 0.02). CONCLUSIONS The toxicity of the BuCy conditioning regimen was lesser than that of Cy+total body irradiation, with the same eradicating capability. Prophylaxis with PTX-MP could prove effective in reducing mucositis.