Dex supports proliferation and inhibits differentiation. Cells from a culture of neonatal cord blood cells were washed 5 days after seeding and aliquots exposed to medium plus Epo, SCF, and Dex (•) or Epo, SCF, and the GR-antagonist ZK 112,993 (▪). (A) Proliferation was monitored by calculating cumulative cell numbers. (B) Hemoglobin accumulation was determined at the days indicated and plotted as milligrams of hemoglobin per 10⁶ cells. (C) At the days indicated by arrows in (A), cell samples from cultures containing Dex (upper panels) or ZK 112,993 (lower panels) were cytocentrifuged onto slides and stained cytochemically with a specific stain for hemoglobin. Well-hemoglobinized cells show a dark to black cytoplasm.