A method of identifying proteins present in human serum which are differentially expressed between normal individuals and patients known two have non-small cell lung cancers and asthma, as diagnosed by a physician, Human serum specimens from each population are digested with trypsin or any other suitable endoproteinase and analyzed using a liquid chromatography electrospray ionization mass spectrometer. Mass spectral data from each population is compared to determine proteins with expression intensities which are significantly differentially expressed between the normal, asthma, and lung cancer populations. Eleven proteins are found to have expression intensities which are significantly differentially expressed between the populations. Finally, the identity of the eleven proteins are obtained by comparing the mass spectral data with known databases having libraries of mass spectral data of known proteins.