By using a custom-made array containing cDNAs preferentially expressed in the mouse embryonic telencephalon (Porteus et al.  Brain Res Mol Brain Res 12:7-22; and Alessandro Bulfone, unpublished data), we studied the gene expression profile of the Dlx1/D1x2-/- subpallium and Pax6 -/- pallium. We identified a transcript corresponding to Unigene Cluster Mm.94021 and rat Evf-1, which is down-regulated in the Dlx1/Dlx2 -/- subpallium and up-regulated in the Pax6-/- pallium. Here, we report the expression pattern of this transcript, designated mouse Evf1 (mEvf1), in the prenatal forebrain of wild-type, Dlx1/Dlx2-/- and Pax6-/- mice using RNA in situ hybridization and reverse transcriptase-polymerase chain reaction. In the wild-type forebrain mEvf1 expression is restricted to the ventral thalamus, hypothalamus, and subpallial telencephalon (caudal, lateral, and medial ganglionic eminences and septal primordia), whereas it is down-regulated in the Dlx1/Dlx2-/- subpallium (mainly in caudal, lateral, and medial ganglionic eminences), and up-regulated in the Pax6-/- lateral and ventral pallium at embryonic day 12.5 and in the dorsal, lateral, and ventral pallium at embryonic day 14.5.