Previous investigations have shown that diethyl ether, halothane and methoxyflurane inhibit the vasoconstrictor response to hypoxia in isolated rat lungs. A damping effect of diethyl ether and halothane has been observed in the human lung as well. In the intact dog lung, however, other workers have recently denied any effect of halothane and enflurane on this vasoconstrictor mechanism. These findings challenged us to investigate the effect of enflurane on the basoconstrictor response to hypoxia in isolated rat lungs. We found that enflurane administered via the airways reduced the response in proportion to the end-tidal concentration of enflurane, as determined by mass spectrometry.