Serum response factor (SRF), a transcription factor known to be essential for early embryonic development as well as post-natal regulation of both cellular proliferation and myogenic differentiation, is expressed broadly in neurons within the adult mammalian central nervous system (CNS). The function of SRF within the developing CNS is not well established, but it is likely to play an important role in neuraxial development and neuronal function, since many of its known target genes (e.g., c-fos) and transcriptional partners (e.g., Elk-1) are also highly expressed in neurons. Immunohistochemical survey of the post-natal developing rat brain revealed a progressive increase in SRF immunoreactivity in neurons of the cerebral and cerebellar cortices, and in selective subcortical regions from birth (P0) through post-natal day 28 (P28). SRF immunoreactivity stabilized from P28 into adulthood. A few loci, such as the nucleus of cranial nerve VII, showed the reverse expression pattern (strong immunoreactivity at P0-P7, declining by P28). The developmental expression pattern of SRF overlaps significantly with that of myotonic dystrophy protein kinase, a potential upstream regulator, and of the LIM-only genes Lmo1, Lmo2 and Lmo3, whose products belong to a family of proteins known to be strong positive regulators of SRF's transcriptional activity. These data suggest that SRF has a significant function in the early post-natal development of the CNS.