We report the data of 19 children with neuroblastoma (NB) or Ewing's sarcoma (EW) who had peripheral blood stem cells (PBSCs) harvested after mobilization by: (1) cyclophosphamide (CY) + etoposide + G-CSF, (2) CY + GM-CSF, or (3) G-CSF alone. There were no consistent differences in the number of PBSCs collected following these three different mobilization regimens as assessed by CFU-GM. 17 patients were reinfused with PBSCs after myeloablative therapy and had successful haemopoietic recovery. These results show that in children with solid tumours such as NB or EW a sufficient number of PBSCs can be collected after G-CSF alone, and that PBSCs collected following stimulation by G-CSF alone are as effective in reconstituting haemopoiesis as those collected after mobilizing chemotherapy + HGFs.