To assess feasibility and potential advantages of PBSC allograft, we transplanted nine patients (age 20-47 years) with advanced or poor-risk hematologic malignancies. These included eight HLA-identical sibling transplants and one partially matched. Cells were collected from donors by apheresis after rh-G-CSF 10-16 micrograms/kg/day for 4-5 days, and stored at 4 degrees C until infusion. Patients were conditioned with busulfan 16 mg/kg and cyclophosphamide 200 mg/kg, and received GVHD prophylaxis with CSA-MTX. The graft consisted of PBSC alone, with a median of 101.2 (range 28-254.2) x 10(4)/kg CFU-GM, 6.84 (range 4.57-15.9) x 10(6)/kg CD34+ cells and 2.5 (range 1.2-6) x 10(8)/kg CD3+ cells. An ANC > 0.5 x 10(9)/1 occurred on (median) day 13 range 11-17), and a platelet count > 50 x 10(9)/l on (median) day 15 (range 12-29) post graft. One patient died of ARDS on day 13, the others are alive 96-485 (median 245) days from the graft. Two patients have relapsed, one of them with isolated CNS involvement. Acute GVHD (grade I-II) occurred in three patients and severe chronic GVHD in six patients, with no relationship to CSA withdrawal. This unexpected incidence of chronic GVHD might be linked to the high number of CD3+ cells in the graft, contributing to a favourable GVL effect.