This study investigates the differentiation of embryonic stem (ES) cells into hematopoietic cells in vitro, simulating the early stages of mouse hematopoiesis. ES cells differentiate into embryoid bodies (EBs) that develop erythroid precursors by day 4 of differentiation, with more than 85% of EBs containing such cells by day 6. The presence of primitive endoderm and mesoderm markers in EBs and embryos indicates a transition from primitive ectoderm to mesoderm to hematopoietic cells. Key genes like GATA-1, GATA-3, and vav are expressed in both EBs and embryos, suggesting their role in early hematopoiesis. Hematopoiesis in EBs occurs without added growth factors and is not significantly influenced by a broad spectrum of factors. However, at days 10 and 14, the addition of Kit ligand and IL-11 enhances hematopoiesis. The kinetics of hematopoietic precursor development, including erythroid, macrophage, neutrophil/macrophage, and mast cell lineages, parallels that in the yolk sac and early fetal liver. The study highlights the reproducibility and efficiency of ES cell differentiation into hematopoietic cells, providing insights into the molecular and cellular mechanisms of early hematopoiesis.This study investigates the differentiation of embryonic stem (ES) cells into hematopoietic cells in vitro, simulating the early stages of mouse hematopoiesis. ES cells differentiate into embryoid bodies (EBs) that develop erythroid precursors by day 4 of differentiation, with more than 85% of EBs containing such cells by day 6. The presence of primitive endoderm and mesoderm markers in EBs and embryos indicates a transition from primitive ectoderm to mesoderm to hematopoietic cells. Key genes like GATA-1, GATA-3, and vav are expressed in both EBs and embryos, suggesting their role in early hematopoiesis. Hematopoiesis in EBs occurs without added growth factors and is not significantly influenced by a broad spectrum of factors. However, at days 10 and 14, the addition of Kit ligand and IL-11 enhances hematopoiesis. The kinetics of hematopoietic precursor development, including erythroid, macrophage, neutrophil/macrophage, and mast cell lineages, parallels that in the yolk sac and early fetal liver. The study highlights the reproducibility and efficiency of ES cell differentiation into hematopoietic cells, providing insights into the molecular and cellular mechanisms of early hematopoiesis.