In the anaesthetized, paralysed and artificially ventilated rabbit the carotid sinus nerve (CSN) has been stimulated electrically for 6 h. At the end of the stimulation period, the carotid body (CB) has been removed, frozen and processed for measurement of the monoamines (MA) and of their catabolites with high-pressure liquid chromatography and electrochemical detection (HPLC-ECD). Results show a significant increase of dopamine (DA) and adrenaline (A) content and of all the metabolites. Besides an important augmentation of DA metabolism suggests that CSN efferent activity exerts some regulation on the MA content and turnover of the CB.