Lung extracts were obtained by either mincing the lungs in saline or by washing the lung with saline through the trachea. The surface tensions of the extracts on compression to 10% of the original area in a surface balance decreased to 7.5 ± 2.1 dynes/cm for rabbits, 10.0 ± 1.8 dynes/cm for dogs, and 6.8 ± 3.8 dynes/cm for man. The surface-active material in the extracts was completely precipitated with trichloroacetic acid. Ethyl or methyl alcohol extracted the activity from the precipitate. By concentrating and chilling the alcohol extract, a very surface-active white precipitate was obtained which was identified as dipalmityl phosphatidyl choline by melting point, chemical analysis, and paper chromatography. Cadmium chloride also precipitated a surface-active complex from the alcohol extract which was identified chemically as dipalmityl phosphatidyl choline. The quantity of hydrolecithin extracted from the lungs was 0.09–0.18% on a wet weight basis. No evidence of the presence of sphingomyelin or other surface-active phospholipid was obtained.