Sixty-one consecutive adult patients with leukaemia, primary myelofibrosis or myelodysplastic syndrome with an HLA-identical or one antigen mismatched family donor were randomised to allogeneic transplantation with PBPC or BM. Progenitor cells were mobilised into the blood by giving the donors 10 microg/kg/day G-CSF subcutaneously for 5-7 days. G-CSF was not given to patients after transplantation. The time to neutrophil counts >0.5 x 109/l was 17 days (95% CI 15.2-18.8 days) in the PBPC group compared to 23 (95% CI 20.3-25.7 days) in the BM group (P = 0.0005). The time to platelet counts >20 x 109/l was 13 days (95% CI 11.7-14.3 days) in the PBPC group and 21 days (95% CI 18.7-23.3 days) in the BM group (P = 0.0005). Acute GVHD of grades II-IV developed in six patients transplanted with PBPC and three patients transplanted with BM. The numbers of patients with chronic GVHD were 15 and 8, respectively. Transplant-related mortality and leukaemia-free survival showed no significant differences. Transplantation with PBPC appears preferable for the recipient due to faster neutrophil and platelet recovery. However, the final conclusion can not be drawn before long-term results on chronic GVHD and relapse incidence in longer randomised trials are available.