To characterise respiratory neurons in the pre-Botzinger complex of adult rats, extracellular recordings were made from 302 respiratory neurons in the ventral respiratory group of sodium pentobarbitone anaesthetised adult rats. Neurons were located 0 to 1.6 mm caudal to the facial nucleus, and ventral to the nucleus ambiguus. The pre-Botzinger complex comprised expiratory neurons (22%, 22/100), inspiratory neurons (37%, 37/100) and phase-spanning neurons (41%, 41/100). In contrast, 80% (125/157) of Botzinger neurons were expiratory, and 80% (36/45) of rostral ventral respiratory group neurons were inspiratory. Rostrocaudally, the pre-Botzinger complex extended about 400 μm, starting at the caudal pole of the nucleus ambiguus compact formation. The pre-Botzinger complex was also characterised by a predominance of propriobulbar neurons (81%, 13/16). Furthermore, 68% (33/48) of expiratory-inspiratory neurons found were located within the pre-Botzinger complex. The variety of neuronal subtypes in the pre-Botzinger complex, including many firing during the expiratory-inspiratory transition is consistent with the hypothesis that this nucleus plays a key role in respiratory rhythm generation in the adult rat.