The restoration of marrow in a mechanically depleted segment of rabbit femur is locally determined and apparently initiated by cells normally resident in bone. This conclusion follows from results of two types of radiation experiments: local x-irradiation of the femur shaft immediately before depopulation and x-irradiation of the total body with exception of the femur diaphysis which was depopulated either just before or after irradiation. In contrast to the rapid initiation of marrow restoration in an unirradiated femur, there was little regeneration during the first 3 weeks in an irradiated femur. Recovery of the shielded depopulated femur in the rabbit that otherwise received total-body irradiation was similar to that in the unirradiated animal. Hence, it would appear that the seeding of circulating hemic stem cells is not essential to repopulation and that cells with hematopoietic potential are present in osseous tissue.