Abstract It is unclear whether myeloid lineages develop within the thymus, or whether their presence relies on trafficking of mature cells from the blood. Recent studies suggested that a multi-potent thymus-homing progenitor gives rise to both lymphoid and myeloid lineages. This conclusion is inconsistent with models of hematopoiesis that include a common lymphoid progenitor (CLP) - a cell that has no myeloid potential but gives rise to all lymphoid populations, including B, T, and NK cells. We have addressed this issue and find that the earliest cells within thymus (commonly referred to as DN1) are lymphoid committed when transplanted in vivo, but when put into certain in vitro conditions, these cells make macrophages and neutrophils. Similarly, CLP, which in vivo are lymphoid committed, when put into these same in vitro conditions, also make myeloid cells at high clonal efficiency. These results bring into question conclusions about the myeloid potential of thymic progenitors that were determined in vitro. To address the source of myeloid populations within the thymus, we asked whether they developed from an intermediate that expressed the RAG recombinase using RAG reporter mice (SVEX). We found that 20% of neutrophils, but very few or no macrophages or dendritic cells within the thymus come from a RAG expressing progenitor. This suggests that a fraction of RAG-expressing progenitors retain neutrophil potential. However, neutrophils make up approximately 0.0001% of the thymus, suggesting that this potential is very limited. Furthermore, we show that separate myeloid committed and lymphoid committed progenitors home to the thymus, suggesting that the myeloid and lymphoid cells within the thymus are mostly, if not entirely derived from separate seeding cells.