Growth factor granulocyte colony-stimulating factor (G-CSF; filgrastim) is effective at progenitor release into the peripheral blood. After high-dose chemotherapy haematopoietic reconstitution occurs after reinfusion of these peripheral blood progenitor cells (PBPC). However, the collection by leukapheresis and further processing of PBPC are very time consuming and expensive. We have studied the transplantation potential of a small volume of unprocessed autologous whole blood after G-CSF mobilisation. Six patients with plasma cell disorders received G-CSF 10 micrograms/kg sc during 6 days. Subsequently 11 of whole blood was collected by phlebotomy, kept unprocessed at room temperature and reinfused 24 h after high-dose melphalan 140 mg/m2. CFU-GM content was 845 per ml blood (median, range 320-3472) and CD34+ cells rose to a median percentage of 0.9 (range 0.4-2.0). Haematological recovery was significantly faster in the study group compared with the control group of 20 patients who received the same dose of melphalan without reinfusion of PBPC. The neutrophil count reached 0.5 x 10(9)/l at a median of 12.5 days after infusion of PBPC vs 38 days in the control group (p = 0.0003). The platelet count reached 20 x 10(9)/l after a median of 23.5 days vs 38 days (p = 0.0218). The shortened recovery was reflected by less transfusions, less antibiotic use and shortening of hospital stay (19 days vs 43 days, p = 0.0003). We conclude that this easy technique of mobilisation and collection of PBPC is very effective for hastening haematologic recovery after high-dose chemotherapy.