Hematopoietic stem cell repopulating ability of WT, mpl^−/−, and Tg(mpl) marrow. WT (Ly5.2), mpl^−/−, and Tg(mpl) marrow competed 1:1 with WT (Ly5.1) marrow cells in lethally irradiated WT (Ly5.1) recipients. The repopulating activity was determined at 16 weeks after transplantation from the percentage of peripheral blood leukocytes in reconstituted chimeras staining for each of the CD45 alloantigens, CD45.1 and CD45.2. Repopulating activity is normalized to the WT (Ly5.1) control marrow; n = 8 to 9 mice for each strain. Means plus or minus SE are shown.