“…Although the neurotransmitters involved in this 'third' nervous system are not yet certain, there is some evidence that neuropeptides may be involved (Barnes, 1984). Non-adrenergic inhibitory nerves have been demonstrated in the lung, particularly in airway smooth muscle (Richardson, 1981) and there is evidence that vasoactive intestinal peptide (VIP) might be a neurotransmitter since VIP has been localised in these nerves by immunocytochemical methods (Dey et al, 1981;Laitinen et al, 1985) and VIP has been found to relax partially airway smooth muscle (Said, 1982;Cameron et al, 1983;Palmer et al, 1985). A NANC inhibitory response has also been 'Author for correspondence at: Department of Clinical Pharmacology,Cardiothoracic Institute,Fulham Road,London SW3 6HP demonstrated in the pulmonary artery of several species (Hamaski et al, 1983b;Frank & Bevan, 1983).…”