The small decrease in airway responsiveness to neurokinin A after administration of lysine acetylsalicylate by inhalation suggests that endogenous prostaglandins may play a contributory protective role in the airway response to neurokinin A in human asthma. Eur Respir J., 1996Respir J., , 9, 1139Respir J., -1145 Sensory neuropeptides, such as substance P (SP) and neurokinin A (NKA), exhibit a range of features which may be relevant to the pathophysiology of asthma, including contraction of airway smooth muscle, increased vascular permeability, mucus secretion and activation of cholinergic neurotransmission [1]. Immunocytochemical studies have demonstrated the presence of sensory neuropeptides and their receptors within the upper and lower airways both in man and rodents [2][3][4]. Although compared with rodents the nerve fibres containing sensory neuropeptides are less dense in human airway tissue, recent studies on necroscopic tissue, bronchoalveolar lavage fluid, and induced sputum have shown increased amounts of SP in the airways of asthmatics compared to controls [5][6][7]. Different authors have demonstrated that both SP and NKA produce dose-related bronchoconstriction when administered by inhalation to asthmatic subjects, NKA being more potent than SP and asthmatic subjects being more responsive than normal subjects [8][9][10][11][12].The mode of action by which sensory neuropeptides elicit bronchoconstriction in asthma is not well understood. The bronchoconstrictor effect of nebulized NKA in asthmatic patients is inhibited by prior treatment with nedocromil sodium [10,13], suggesting that this response may be evoked indirectly rather than through direct stimulation of airway smooth muscle. There is some support for an action of sensory neuropeptides in eliciting prostaglandin synthesis. Recent in vitro studies support the view that many of the biological responses of the sensory neuropeptides may result from the local release of bioactive prostanoids [14][15][16].In line with the notion that administration of bronchoactive drugs by inhalation achieves maximum effect with smaller doses, BIANCO and co-workers [17,18] have recently shown that the potent cyclooxygenase inhibitor, aspirin administered as an aerosol of lysine acetylsalicylate (L-ASA) solution elicits better protection against nonspecific stimuli in the airways of asthmatics than when given orally. Using this alternative experimental approach, we intend to expand our previous observations with other nonspecific agonists [19,20], by evaluating the relative contribution of contractile prostaglandins to the airway response provoked by inhaled NKA in asthmatic subjects.