Expression of MR SCF in Sl/Sl^d mice improves red cell production. Total red cells were compared betweenSl/Sl^d (n = 16), Sl/Sl^d-S (n = 10), Sl/Sl^d-MR (n = 13), and wt (n = 20) mice. All black-eyed white mice and wt mice at 12 weeks of age were tail bled, and their RBC counts/mL were determined as described in Materials and Methods. Total red cells in each animal were calculated by multiplying the mean blood volume of an adult animal; (3.15 mL/100 g)55 by the total body weight (in grams) and the RBC counts per mL. The results show mean (×10⁹) ± SEM (bars). (∗) P = .01 ,Sl/Sl^d-MR versus Sl/Sl^dand Sl/Sl^d-S.