Lung surfactant protein B, SP-B, is found at the air-water interface of the lung. A deficiency in SP-B at birth is known to be fatal. We have recently successfully studied the ozone-initiated oxidation of the N-terminal portion of SP-B, SP-B1¿25, at the air-water interface and shown that parts of the peptide reacts rapidly with ozone and the reaction leads to a change in surface structure. Surface pressure measurements indicate that the oxidized peptide has different surface properties to the native forms. In this work we propose to study the surface properties of monolayers of lung lipid DPPC and SP-B(1-25) after exposure to gas phase ozone. We wish to ascertain whether the oxidized peptide is more readily squeezed out of the monolayer than SP-B(1-25) itself and how readily the oxidized peptide is re-adsorbed to the interface when the surface pressure is decreased.