Six patients with high-risk leukaemia received a myeloablative regimen followed by allogeneic peripheral blood progenitor cells transplantation (PBPCT) from an HLA-identical sibling donor. Donors received 10-12 mu g/kg/day of G-CSF subcutaneously for 5 days. G-CSF was well tolerated except for moderate bone pain. Peripheral blood leukapheresis product contained 1-4 times more CD34+ cells and approximately a log more of T lymphocytes than marrow grafts from normal donors. In the two first cases the leukapheresis product was partially depleted of T-lymphocytes using counterflow centrifugation. No growth-factors were administered post-transplant. GVHD prophylaxis consisted of cyclosporin A (CyA) in one case, and CyA and methotrexate in five cases. All patients engrafted with a neutrophil count reaching more than 0.5 x 10(9)/L by day 12 to 21 post-transplant and a platelet count above 20 x 10(9)/L by day 6 to 41 post-transplant. Acute GVHD was clinical grade 0 (n = 2), I (n = 1), II (n = I), grade III (n = I) and grade IV (n = 1). One case presents an extensive chronic cutaneous GVHD and is currently being treated with methylprednisolone. In conclusion, allogeneic transplants using PBPC can be performed safely. This may result in a rapid neutrophil and platelet engraftment, without an apparent increased risk of GVHD.