We have analysed the clinical course of the 14 consecutive allogeneic peripheral blood stem cell transplantations (PBSCT) and cellular composition of the grafts. Donors were HLA-identical siblings except for the one donor who was only HLA-phenotypically identical brother. Nine of them were sex-mismatched to their recipient. Donors received filgrastim (G-CSF) at a dose of 10 microkilograms/kg for 5 days (4-6). Leukaphereses were started at 5 day to obtain the target dose 4 x 10(6) CD34+ cells/kg recipient weight. Median 24 l of blood (24-36) was processed collecting: 10.3 x 10(8)/kg (6.69-18.8) WBC, 9.9 x 10(8)/kg (5.87-16.02) MNC, 9.72 x 10(6)/kg (0.74-18.98) CD34+ cells, 242.5 x 10(6)/kg (77.9-422) T lymphocytes (CD4+ to CD8+ ratio was 1.5), 76 x 10(6)/kg (24-113) B lymphocytes, 33 x 10(6)/kg (14-88) NK cells and 168.8 x 104/kg (23.1-271.4) CFU-GM with 131.7 x 10(4)/kg (8.4-297.6) BFU-E. Engraftment times to a neutrophil count (ANC) > 0.5 x 10(9)/l was achieved at a median of 15 days (range 10-23) in all patients whereas the platelet count > 20 x 10(9)/l at a median of 14 days (9-19) in all but one patient who received the smallest dose of CD34+ cells. Acute graft versus host disease (GvHD) developed in 8 patients who survived more than 30 days. Most of them (75%) were patients with chronic myeloid leukaemia (CML). In 4 of them GvHD was steroid resistant. Chronic GvHD developed in 3 of 6 evaluable patients. We confirm that allogeneic PBSCT result in rapid and longterm trilineage engraftment. However, the observation of the increasing incidence and severity of acute GvHD in patients with CML will require verification in the larger setting of patients after completion of ongoing clinical trials.