The haematopoietic growth factor (HGF), granulocyte colony stimulating factor (G-CSF; filgrastim) substantially shortens the period of severe neutropenia that follows high-dose chemotherapy and autologous bone marrow infusion by stimulating granulopoiesis. Filgrastim also increases numbers of circulating progenitor cells. We have studied the ability of filgrastim to mobilise peripheral blood progenitor cells (PBPC) and assessed their efficacy when infused after chemotherapy on recovery of neutrophil and platelet counts. Seventeen patients with non-myeloid malignant disorders received filgrastim (12 micrograms/kg daily for six days) by continuous subcutaneous infusion. Numbers of granulocyte-macrophage progenitors in peripheral blood increased a median of 58-fold over pretreatment values, and numbers of erythroid progenitors increased a median of 24-fold. Three leukapheresis procedures collected a mean total of 33 (SEM 5.7) x 10(4) granulocyte-macrophage progenitors per kg body weight. After high-dose chemotherapy in 14 of the patients (busulphan and cyclophosphamide), these cells were used to augment autologous bone marrow rescue and post-transplant filgrastim treatment. Platelet recovery was significantly faster in these patients than in controls who received the same treatment apart from the infusion of peripheral blood progenitors; the platelet count reached 50 x 10(9)/L a median of 15 days after infusion of haematopoietic cells in the study patients compared with 39 days in controls (p = 0.0006). The accelerated neutrophil recovery associated with filgrastim treatment after chemotherapy was maintained. Subsequently, 10 patients received filgrastim-mobilised PBPC without marrow after high-dose chemotherapy. The rate of platelet and neutrophil recovery in these patients was at least equal to that observed in the patients receiving PBPC and bone marrow.(ABSTRACT TRUNCATED AT 250 WORDS)