During haematopoiesis in Drosophila embryos, prohaemocytes in the head mesoderm differentiate mainly into plasmocytes, as specified by the transcription factors Glial cells missing (GCM) and GCM2, and into crystal cells, which requires the RUNX transcription factor Lozenge (LZ). On p. 4635, Batailléand colleagues report that a dynamic interplay between GCM/GCM2 and LZ determines the fate of bipotent prohaemocytes in Drosophila embryos. The researchers show that gcm is initially expressed in all prohaemocytes but that its downregulation in the anterior-most row of prohaemocytes is required for the initiation of lz expression. The differentiation of the lz-expressing precursors into crystal cells or plasmocytes is subsequently regulated by gcm/gcm2 activity. However, lz does not repress gcm. Thus, the transition from a bipotent haematopoietic precursor to lineage-restricted precursors in Drosophila embryos does not rely on reciprocal antagonism between two lineage-specific transcription factors, unlike some cell fate decisions during mammalian haematopoiesis.