Lhx5,the mouse ortholog of theXenopus Xlim-5,is a LIM/homeobox gene expressed in the central nervous system during both embryonic development and adulthood. During development its domain of expression is mainly localized at the most anterior portion of the neural tube, and it precedes the morphological differentiation of the forebrain; for this reason we believe thatLhx5could play an important role in forebrain patterning. Here we present the structural organization and the chromosomal localization of theLhx5gene. The gene is composed of five exons spanning more than 10 kb of genomic sequence. The first and second LIM domains are encoded by the first and second exon, while the codons of the homeobox are split between the third and the fourth exons. The structure ofLhx5is similar to that of other LIM/homeodomain proteins,Lhx1/lim1andLhx3/lim3,but differs from that of other LIM genes, such asmec3and LMO1/Rbtn1,in which the codons for the LIM domains are interrupted by introns. We have mappedLhx5to the central region of mouse chromosome 5.