In the article “Distinguishing between Directional Guidance and Motility Regulation in Neuronal Migration,” by Michael Ward, Corey McCann, Michael DeWulf, Jane Y. Wu, and Yi Rao, which appeared on pages 5170–5177 of the June 15, 2003 issue, it is incorrectly stated that mSlit1 was used in all experiments. The authors want to clarify that in fact, human Slit2 was used in all experiments.