Relapsed or very aggressive high-grade NHL and refractory low-grade NHL have a poor clinical outcome. Autologous BMT may be used but is of limited efficacy in these cases. Allogeneic BMT offers the advantage of tumour-free bone marrow and a possible GVL effect. Between 1987 and 1996, 13 patients (median age 31 years) suffering from lymphoid malignancies underwent allo-BMT. Four patients had low-grade NHL, three intermediate-grade and six high-grade NHL. Three patients were grafted with evolutive disease, four were in partial remission after several courses of chemotherapy, two were in CR2 and four were in CR1 after initial therapy. The mean number of prior treatments was 2.7 (1-6). Median time from diagnosis to BMT was 25 months (4-90). The conditioning regimen consisted of cyclophosphamide (120 mg/kg/day for all, plus VP16 in one case) and total body irradiation. Five out of the seven patients who were not in CR at the time of transplantation entered CR after BMT. Eight patients developed acute GVHD grade > or = II and four had chronic GVHD. Nine patients are alive, eight in CR with a median follow-up of 49.8 months post BMT (2-125). Overall survival is 67.3% and the median time for EFS is 102 months. Two patients with low-grade NHL relapsed 61 and 102 months post BMT and were treated with DLI. One patient with a stage IV SLL had a partial remission and one with multiple cutaneous localisation of FL entered CR after grade IV acute GVHD. Allo-BMT is a highly effective treatment for advanced poor prognosis lymphoid malignancies with acceptable toxicity. Moreover, DLI can be effective in relapsing patients.