Three-color flow cytometric analysis of thymocytes of C.B.-17 scid mice injected with freshly prepared primitive marrow progenitors or pooled primary colonies. Five thousand enriched marrow cells (left) or the equivalent of 40 pooled primary colonies (right) were injected intravenously into scid mice. On days 15, 20, 25, and 60 after cell transfer, thymocytes were analyzed for Ly-1.1, CD4, and CD8. The expression of Ly-1.1 on whole thymocytes and that of CD4 and CD8 on Ly-1.1⁺ cells at each time is shown.