Total human (CD45/71⁺) and mature erythroid (glycophorin A⁺) cells in NOD/SCID mice transplanted with equivalent grafts of human fetal liver, cord blood, or adult marrow cells and then injected with recombinant human growth factors (▪) or not (□) as described in the text. The difference plus and minus growth factors for all pairs was not significant (P > .05) except for glycophorin A⁺ cells in the mice transplanted with adult marrow (P << .001).