Blood drawn from one animal treated with G-CSF alone (100 μg/kg × 5 days) and from one animal treated with G-CSF plus FL for 5 days was drawn at day 6 of treatment. Suspension cultures of mononuclear cells (A and B) and of purified CD34 cells (C) from these mononuclear cells were set up, and cellular proliferation and expansion of progenitors were monitored for 2 weeks. Note the higher proliferative response (A) and accumulation of progenitors (B) in the G-CSF plus FL animal compared with G-CSF alone. In C the proliferative response for 4 weeks of CD34⁺ cells (∼70% CD34⁺) enriched from PBMC of the G-CSF plus FL animal and the expansion of CFC for 1 and 2 weeks in culture is shown. Similar data from G-CSF–only treated animal could not be generated, as the enrichment of CD34⁺ cells was poor and their total number was low.