Haploidentical transplantation has become a clinical option for patients lacking a compatible donor. However, patients are still referred at advanced stages and are usually heavily pretreated. This results in a high risk of toxicity, relapses and infections. We therefore started a donor lymphocyte infusion (DLI) dose-finding protocol, to try to improve both relapse rate and immunity reconstitution. In all, 12 consecutive patients were investigated. All had a refractory, some progressive, disease. Conditioning consisted of TBI, melphalan, ATG, fludarabine and CSA pretransplant. In four rapidly progressive patients, Ara-C had to be given 1 week preconditioning. The graft was T- and B-cell depleted with a fixed reinfused CD3 dose of 5 x 10(4)/kg. All patients engrafted before day 20. G-CSF was given from day 5 post-transplant and replaced with GM-CSF in the last three patients. Nonrelapse related mortality was 0/12 at 1 year. DLI were started at day 28 (3 x 10(4) CD3/kg) in the two first patients. This resulted in acute graft-versus-host disease (aGVHD) and chronic graft-versus-host disease (cGVHD) in both, but they did not relapse. The next dose was 1 x 10(4)/kg monthly for 3 months. This was well tolerated with only one grade I GVHD. Given the high relapse rate, we escalated doses (1, 3 and 10 x 10(4)/kg). This produced GVHD in all. We next moved, to GM-CSF and 1 x 10(4) CD3/kg monthly. Overall, 6/12 patients relapsed and received therapeutic DLI, starting at 1 x 10(5) CD3/kg with escalation every 2 weeks. We conclude that prophylactic DLI are feasible in adult haploidentical transplantation, without GVHD at a monthly dose of 1 x 10(4) CD3/kg. They result in faster CD4 recovery and a low rate of infections. The impact of GM-CSF remains to be further investigated. This scheme seems ideal for patients transplanted early in the course of their disease. In very bad prognosis patients, it remains insufficient to rapidly induce a GVL effect. Escalated doses are feasible but the price is aGVHD. Therapeutic DLI can be given at higher doses, depending on the time post-transplant. Haploidentical transplantation with low-dose DLI is a safe procedure that should be considered in all patients needing a transplant, but lacking a matched donor, early in the course of the disease.