Despite prophylaxis with immunosuppressive drugs, severe graft-versus-host disease (GVHD) remains a major cause of morbidity and mortality following allogeneic stem cell transplantation. T cell depletion of the graft has decreased incidence and severity of GVHD but has resulted in a higher incidence of graft failure and relapse. To reduce the risk of severe GVHD, but at the same time to maintain the graft-versus-tumor effect, we administered a fixed low number of 1 x 10(5) donor T cells per kilogram of body weight to recipients of CD34(+) cell-enriched allogeneic peripheral blood stem cells (PBSCs). Donor lymphocyte infusions (DLI) were then given in incremental doses when mixed chimerism persisted or signs of relapse occurred. A total of 23 patients receiving allografts from related and unrelated donors were treated according to this protocol after myeloablative or reduced intensity conditioning. One patient did not engraft and 3/20 evaluable patients developed acute (a) GVHD > or = grade II, with a corresponding estimated cumulative incidence of 15.6% (95% CI 0-30.5%). DLI (n = 13) induced aGVHD > or = II in 6 patients, but the severity of the syndrome was reduced. Overall GVHD-related mortality was low (13%). The probability of disease-free survival and overall survival at 2 years was 0.40 (95% CI 0.21-0.75) and 0.36 (95% CI 0.21-0.63). Progression-free survival and overall survival was significantly better in patients with acute or chronic myelogenous leukemia compared to patients with lymphoproliferative disorders (p = 0.002; p = 0.02). We conclude that the combination of allografts with a T cell content of about 1 x 10(5)/kg and escalating doses of DLI is a viable transplant strategy in patients with myeloid leukemias, which results in stable engraftment and a reduction of mortality from aGVHD.