All mature blood lineages in the peripheral circulation are derived from pluripotent haematopoietic stem cell. Progressive lineage-restriction of this stem cell is executed, in part, by the interplay and cross-talk between a host of lineage-restricted as well as ubiquitous transcription factors. To elucidate the regulatory mechanisms underlying the erythroid gene regulation, it is essential to understand how individual transcription factors contribute to the regulation of specific target genes, and how these erythroid transcription factor genes are regulated in turn. These key issues of mammalian development have been addressed by examining the activities controlling the prototype transcription factor, GATA-1. The transcriptional, regulation of GATA-1 has been intensively investigated, thereby leading to the identification of its developmental stage-specific regulatory sequences. Loss-of-function mutant animals, combined with specific marking of the primitive and definitive erythroid lineages have also shed new insight into how GATA-1 activity is required in viva at specific developmental stages. Procedures have also been developed for ascertaining whether or not the GATA-1 protein actually binds in vivo to regulatory GATA motifs in candidate target genes. Application of a similar multifaceted approach should enable investigators to examine the physiological roles that any transcription factor might play in vivo during the differentiation of any well defined cell lineage.