The reactivity of cat lung parenchymal strips to histamine and acetylcholine in vitro was studied at various stages of inflammation of the airways induced experimentally by the intratracheal administration of turpentine oil or Staphylococcus aureus, both in aerosol form. With histamine, the contractile responses of the lung strips were enhanced depending on the stage of turpentine oil inflammation. Similarly, the lung strips responded more to histamine in the staphylococcal inflammation. The reactivity of the lung strips to acetylcholine remained mainly unaffected by either type of inflammation.