Between February 1998 and October 1999, 24 patients with advanced leukemia, lymphoma or solid tumors received G-CSF mobilized peripheral blood stem cells (PBSC) from HLA-matched sibling donors after dose-reduced conditioning therapy. Only patients with reduced performance status or major infectious complications, not eligible for standard transplant procedures, were included. The 5-day conditioning therapy consisted of 3.3 mg/kg intravenous busulphan x 2 days and 30 mg/m2 fludarabine x 5 days. GVHD prophylaxis was performed with either CsA alone (n = 5), CsA combined with short course methotrexate (n = 5) or mycophenolate mofetil (n = 14). The day 100 survival was 95.2% for the whole group. All patients engrafted after a median of 15 days (range, 11-19) and 12.5 days (range, 10-19) for neutrophils and platelets, respectively. The median time to a neutrophil count of <0.5 x 109/l was 7 days (range, 2 to 12). Acute GVHD >I was observed in six patients, whereas eight patients have signs of chronic GVHD. The prospective 12 month overall survival with a median follow-up of 7 months is 63%. Relapse of disease and toxicity associated with chronic GVHD were the main causes of death. The treatment-related mortality was 12.5%. Dose-reduced conditioning using intravenous busulphan and fludarabine allows stable engraftment without ATG in related transplants and leads to a reduction of transplant-related mortality.