Unmodified allogeneic peripheral blood stem cell transplantation (alloPBSCT) was performed in 20 consecutive acute non-lymphoblastic leukemia (ANLL) patients from their HLA-identical siblings. There were 11 males and 9 females. Median age was 34 years (range 17-43). Donors were primed with 2.5-15 micrograms/kg/day s.c. granulocyte-colony stimulating factor (G-CSF, Neupogen, Roche). Conditioning regimen was Bu (16 mg/kg) + Cy (120 mg/kg) in 19 patients and high dose Ara-C (3 gr/m2 twice daily for 3 days) for one patient who relapsed after bone marrow transplantation. Eighteen patients were in CR1. CsA + short-term MTX (n = 19) or CsA alone (n = 1) were used for graft versus host disease (GVHD) prophylaxis. The median number of apheresis procedures for each patient was 2 (2-4). A median of 6.5 (3.2-38.2) x 10(8)/kg MNC or 9.4 (2.2-12.4) x 10(6)/kg CD34+ cells were given. Median days to reach granulocyte of > 0.5 x 10(9)/l and platelet of > 50 x 10(9)/l were 12 (10-14) and 15 (11-35) respectively. Day 100 transplant-related mortality was 20 per cent (4/20). Grade 2 to 4 AGVHD was seen in 8 out of 17 (47%) evaluable patients. Severe AGVHD occurred in 3 out of 17 (18%). Clinical CGVHD of all grades developed in 12 out of 17 (70%) evaluable patients. The mean disease-free survival and overall survival were 17 (range: 8-33 months) and 18 months (range: 10-34 months), respectively. In conclusion, alloPBSCT in ANLL is associated with a faster engraftment, no greater incidence of AGVHD, but increased risk of CGVHD.