The Robo genes encode a family of proteins that are the receptors for the midline repellent Slits and play a role in axon guidance. In addition to Robo1 and Robo2, Rig-1 has been recently identified in mouse as a novel member of the Robo family of proteins. As a first step in elucidating the role of Rig-1 during vertebrate development, we characterised the expression of Rig-1 by in situ hybridisation together with Robo1 and Robo2 in the spinal cord and other tissues of the mouse embryo. Our results show that Rig-1 has a dynamic pattern of expression in the developing CNS. In the spinal cord Rig-1 shows overlapping but distinct pattern of expression with Robo1 and Robo2.