The current chicken genome build contains only a single colony-stimulating factor (CSF) gene, granulocyte/macrophage (GM)-CSF (CSF2). However, genes encoding receptors for two other CSFs, G-CSF (CSF3) and M-CSF (CSF1), are present in the genome. Another apparently chicken-specific CSF, myelomonocytic growth factor (MGF), shares substantial sequence homology with mammalian CSF3 but is absent from the genome. The putative region of the chicken genome that should contain the CSF3 ortholog, while not currently mapped to a specific chromosome, exhibits considerable conserved synteny with loci containing this gene in several other species. In silico analysis of the predicted CSF3 location revealed a large region homologous with the MGF promoter, upstream of a large sequence gap. In view of the many structural and functional features common to both MGF and huCSF3, we predicted that MGF is in fact CSF3 and its gene would be located within the sequence gap. To validate this hypothesis, a primer walking strategy was used to bridge the genomic sequence gap. Full-length sequencing of the entire region and thorough, detailed analysis of the coding region confirmed that the MGF gene lay within this sequence gap, and therefore that it should be renamed CSF3.