Background: MafK serves as a required subunit of erythroid transcription factor NF-E2 and also functions with various heterodimeric CNC family proteins. Mark expression begins in early mesoderm and is observed in mesenchymal and haematopoietic cells, as well as in neurones during mouse development. In mesodermal descendants, MafK mRNA begins with a distal first exon (called I(M)), whereas the mRNA in neurones begins with a proximal first exon (I(N)). Results: To elucidate the mechanisms that underlie the tissue- specific transcription of the mafK gene, and to gain insights into the functions of MafK during neural development, we analysed the activity of the mafK I(N) promoter. A detailed investigation of mark expression in the embryonic spinal cord revealed that I(N)-initiated mRNA is expressed in the ventral side of the spinal cord. Transient transfection analysis of reporter plasmids bearing the IN promoter and upstream regions revealed that the 'core' region of this promoter (nt -67 to -9) is active and that its integrity is crucial for this activity. The core region was also capable of directing the tissue-specific transcription of a reporter gene in neural cells of the spinal cord in transgenic mice in vivo. Conclusion: These results demonstrate that the specific expression of mafK in neural cells is determined, at least in part, by the core region of the I(N) promoter.