Airway function deteriorates significantly on cessation of exercise or isocapnic hyperventilation challenges but is largely preserved during the challenge in humans and guinea pigs. PGE₂, an endogenous bronchodilator, might be responsible for the preservation of lung function during hyperventilation (HV). We hypothesized that PGE₂ might have a protective effect during HV, partially explaining the minimal changes in respiratory system resistance (Rrs) usually seen during HV in humans and guinea pigs. Therefore, changes in Rrs were measured during and after HV in anesthetized, mechanically ventilated guinea pigs treated with flurbiprofen (FBN) or placebo. With HV, there was an initial bronchodilation that was unaffected by FBN. Rrs then increased with time during HV, an effect that was blocked by FBN. After HV, Rrs increased further in all groups, but the increase in Rrs was less in the FBN-treated groups. FBN treatment reduced the PGE₂ concentration slightly in lung lavage fluid compared with placebo. We found no enhancement or refractoriness of the Rrs response to repeat bouts of HV and no effect of FBN treatment on the response of Rrs to repeat HV. These results suggest that a constrictor PG is released during and possibly after HV and that the post-HV increase in Rrs is the sum of effects of the PG released during HV and a second constrictor mechanism operating after HV. We found no evidence for bronchodilator PG during or after HV in the guinea pig.