SLIT and NTRK-like family 4 (Slitrk4) is a member a protein family consisting of six homologous transmembrane proteins (Slitrk1-6) that share two conserved leucine-rich repeat domains in the extracellular domain and have significant homology to Slit, a secreted axonal growth-controlling protein. These proteins are also homologous to trk neurotrophin receptors in their intracellular domains (1). Expression of Slitrk proteins is highly restricted to neural and brain tumor tissues, but varies within the protein family (1,2). Like every other Slitrk protein except Slitrk1, overexpression of Slitrk4 inhibited neurite outgrowth in cultured neurons, suggesting that these proteins are involved in the control of neurite outgrowth. This antibody is predicted to have no cross-reactivity to other Slitrk proteins.