The retrotrapezoid nucleus (RTN), recently described in the cat, is an anatomically identified cell group of the ventral medulla. It is of interest because of its possible role in the generation or control of breathing. The present investigation confirms the existence in the rat of an analogous cell group, as identified by retrograde transport of rhodamine microbeads from an injection site in the ventral respiratory group of the ventral medulla. Electrophysiological recordings from the region of RTN reveal individual units with respiratory related activity. These results support a possible role for the RTN in the control of breathing.