In six anesthetized, paralyzed, mechanically ventilated pigs we evaluated the respiratory effects of inhaled nitric oxide (NO) (80 ppm in O2) under control conditions and after platelet-activating factor (PAF) administration (50 ng/kg, i.v.). PAF was also administered to the same pigs after pretreatment with indomethacin (3 mg/kg, i.v.). The mechanical properties of the respiratory system were evaluated by the rapid airway occlusion technique. With this technique the overall respiratory resistances, the airway resistances, and the additional resistances of respiratory system and lung can be evaluated. The results show that NO inhaled by the pig at 80 ppm for 6 min under control conditions reduced static and dynamic elastances of the respiratory system and lung and pulmonary arterial pressure, without modifying bronchomotor tone. Therefore, NO reduced the PAF-dependent changes in resistances and in static and dynamic elastances of the respiratory system and lung. The modest change in elastances caused by PAF in pigs pretreated with indomethacin was reduced by NO inhalation, which also has a mild bronchodilatory effect. The changes in elastances appear to be correlated with the pulmonary vasodilator activity of inhaled NO.