The number of GFP-positive cells in the kidney of wt-Epo-GFP transgenic mouse is increased as the hematocrit is decreased. Various levels of anemia were induced in wt-Epo-GFP transgenic mice (line WA) by bleeding over 2 days and kidney sections were taken. The plasma Epo concentrations () and the numbers of GFP-positive cells in the kidney sections (•) increased as the hematocrit (Hct) decreased.