Latexin is a novel 29 kDa protein which is expressed in a subpopulation of neurones in the lateral cerebral cortex of adult rats. Here, we report the distribution of immunohistochemically detectable latexin in the rat brain during early phases of development. Latexin was first detected at embryonic day 11 (E11) along the dorsal midline of the diencephalon. At E12, the expression domain of latexin corresponded to the dorsal midline regions of the diencephalon and also of the mesencephalon. At E14, the expression domain was more restricted than that at E12. Strong latexin expression was restricted within the pineal anlage, and dorsal midline cells anterior to the pineal anlage did not express latexin. These findings suggest that latexin plays a role in regional specification and/or morphogenesis of the forebrain, especially of its dorsal midline structures including the pineal gland.