Connexins are structural proteins that are part of the gap junctional channels which couple cells in different tissues. Connexin36 (Cx36) is a new member of the connexin gene family, found to be expressed essentially if not exclusively in neuronal cells in adult CNS of mouse, rat and man. Here we have studied Cx36 expression during murine embryonic development. Cx36 shows a highly dynamic pattern of expression. It is first (E9.5) evident in the forebrain and later its expression expand caudally in the midbrain. At E12.5 its expression correlates with major morphogenetic boundaries in the developing mouse brain, specifically with the dorsoventral telencephalic boundary and the Zona Limitans Intrathalamica. Starting at midgestation (E12.5), it is also expressed in both sympathetic and spinal ganglia, and in two longitudinal stripes along the spinal cord.