We tested the hypothesis that oleic acid-induced acute lung injury activates pulmonary nociceptors, that is, C fibre receptors (CFRs) and high-threshold Adelta fibre receptors (HTARs). Single-unit activity was recorded in the cervical vagus nerve and assessed before and after injecting oleic acid (75 microl kg(-1) i.v.) into anaesthetized, open-chest, mechanically ventilated rabbits. Unit activities increased within seconds and peaked within a few minutes (from 0.3 +/- 0.1 to 1.4 +/- 0.9 impulses s(-1) for CFRs and from 0.5 +/- 0.1 to 1.7 +/- 0.3 impulses s(-1) for HTARs, both n = 8 and P < 0.05). These activities were sustained while pulmonary oedema developed and dynamic lung compliance decreased over the 90 min observation period. Activities in slowly adapting receptors and rapidly adapting receptors were also increased; however, their responsiveness to airway pressure stimulation decreased progressively. We conclude that pulmonary nociceptors are stimulated during acute lung injury. The dual nociceptor system, consisting of both non-myelinated CFRs and myelinated HTARs, may play an important role in the pathophysiological process of acute lung injury-induced respiratory responses.