Competitive repopulation of HBD and normal marrow against normal congenic marrow. In two independent experiments (A and B), mixtures of either mutant and congenic or normal and congenic marrow were injected into irradiated C57BL6/J-+^hbd/+^hbd, Gpi1^a/Gpi1^a, Igh^a/Igh^a, Thy1^a/Thy1^a recipient mice. The percentage of isotype Gpi1b in the peripheral RBCs and leukocytes indicated the competitive ability of the mutant or normal marrows compared with congenic marrow. Data points indicate the mean for mixtures as indicated under the figure. Error bars represent the SEM. In (A), n = 6 for both the normal:congenic mix and HBD:congenic mixes. The P value for the leukocytes for the HBD:congenic versus the normal:congenic was .0007 at 24 weeks posttransplantation. In (B), n = 6 for normal:congenic and HBD:congenic mixes. At 16 weeks, n = 5 and at 24 weeks n = 4 for normal:congenic mix. The P value for HBD:congenic versus normal:congenic leukocytes was 0.27 at 24 weeks.