The present study was carried out to investigate the possibility that noradrenaline (NA) and neuropeptide Y (NPY) are co-released after afferent vagal or saphenous stimulation (1, 5, 10 and 20 Hz) in chloralose-anaesthetized dogs. Electrical stimulation of the vagus elicited an increase in plasma NA levels for the 5, 10 and 20 (but not 1) Hz frequencies. Blood pressure only increased after a 20-Hz stimulation. In contrast, no change in plasma NPY levels was observed whatever the frequency of stimulation. Electrical stimulation of the saphenous nerve failed to change plasma NA and NPY levels. The present data suggest that (1) the release of NA varies according to the frequency of stimulation of nociceptive fibres, (2) NPY release does not seem to be involved in the pressor effect elicited by the stimulation of nociceptive-sensitive fibres, and (3) NPY and NA release are not necessarily linked.