Levels of reconstitution of irradiated +/+ recipients of low numbers of 14.5-dpc W⁴¹/W⁴¹ or +/+ FL cells in a standard CRU assay protocol. Values shown are the proportion of W⁴¹/W⁴¹-derived or +/+-derived WBCs at either 6 to 8 or 16 to 20 weeks posttransplant in individual positive recipients from groups in which ≥37% of the mice were negative when examined at either 6 to 8 or 16 to 20 weeks posttransplantation. Some of the values shown for recipients injected with +/+ FL cells have been taken from a previous publication.36