We studied 25 mongrel dogs who were anaesthetized and their lungs ventilated for investigation of the effects of pancuronium on pulmonary arterial pressure (PAP) in the normal lung, in oleic acid-induced lung injury and in lung injury with hypoxaemia. In the normal lung, PAP was not affected by pancuronium. During lung injury, however, PAP was increased from 21.5 (SD 2.8) to 24.6 (4.2) mm Hg (P < 0.01) and from 22.0 (4.2) to 27.0 (5.8) mm Hg (P < 0.01) after pancuronium 0.08 mg kg-1 and 0.16 mg kg-1, respectively, and from 26.0 (2.9) to 37.1 (3.1) mm Hg after pancuronium 0.16 mg kg-1 when hypoxaemia was present (P < 0.01). The increase in PAP induced by pancuronium was associated with increases in cardiac output and pulmonary vascular resistance. Pretreatment with phentolamine attenuated the pancuronium-induced increase in PAP. The increase in PAP induced by pancuronium was also reduced by vagotomy. If these results in dogs are relevant clinically, then pancuronium should be avoided as a neuromuscular blocker in lung injury.