To circumvent aGVHD in the early phase after allogeneic stem cell transplantation but to provide GVL activity later on, we performed alloPBSCT with CD34+ selected grafts followed by delayed add-back of CD3+ T cells. Ten consecutive patients having an HLA-identical sibling donor were enrolled on to this trial. Four patients were in first CR of high-risk ALL, another four in first CR of AML, one was in second myeloid blast crisis of CML, and one was in PR of relapsed NHL. Conditioning consisted of 2 x 60 mg/kg CY plus 12 Gy TBI. G-CSF (Filgrastim) mobilized peripheral cells were CD34+ selected using the Isolex 300i system in nine patients and the CliniMacs system in one. Median CD34+ purity was 86%. A median of 2.8 x 10(6)/kg CD34+ cells were transplanted. The number of CD3+ cells in the allografts was 5.7 x 10(4)/kg (median) after Isolex 300i, and 0.2 x 10(4)/kg after CliniMacs. All patients received G-CSF (Filgrastim) and engrafted rapidly. Standard-dose CsA was administered, and until day +60 no aGVHD occurred. At that time point, seven patients received 2 x 10(6)/kg CD3+ cells while CsA had been tapered to 50% of the starting dose. One of these patients died after a second T cell boost given on day +90 without concomitant immunosuppression due to grade IV intestinal aGVHD. Three others developed cutaneous cGVHD. Taken together, T cell depletion by CD34+ selection does not impair rapid engraftment in the HLA-identical sibling donor setting. Using standard-dose CsA the risk for acute GVHD seems to be minimized. Add-back of 2 x 10(6)/kg CD3+ cells on day +60 with CsA protection is feasible. However, whether this is the optimal time point and number of T cells remain to be further elucidated.