Lipid analyses of the bronchoalveolar washing fluid of three patients affected with chronic unidentified pneumonia showed the presence of a major hydrophobic compound identified as paraffin oil by thin layer chromatography, infrared spectroscopy and gas liquid chromatography (by comparison with various paraffin preparations as standards). Moreover the phospholipid and neutral lipid composition was determined. In conclusion, the usefulness of bronchoalveolar lavage and its biochemical analysis is discussed as a non-invasive method of diagnosis and therapeutic approach to liquid paraffin pneumonia (in the cases herein described, between 100 and 500 mg of paraffin oil were extracted from 100 ml of bronchoalveolar washing fluid.