Over the past three decades, a number of myeloid cell lines have been established and have proven useful for the study of various aspects of normal and disordered hematopoiesis. However, one myeloid lineage for which a useful cell line model has been sorely lacking is the eosinophil. We review the characteristics of the recently developed AML14 and AML14.3D10 cell lines and summarize how they have been used to obtain important new information relevant to eosinophil biology. Observations regarding the apparent ability of the AML14.3D10 cell line to “switch” lineages and to produce and use GM-CSF in an autocrine fashion are also reviewed.