Another point of research concerning SP-A is the diagnostic value of this molecule, the expression of which is restricted to the lungs. It has been reported that SP-A levels in BAL or serum from patients suffering from idiopathic pulmonary fibrosis correlate with the progression of the disease and can be used to predict survival [34, 38] . In samples from airway secretions SP-A measurements are described to be useful also for the diagnostics of pulmonary edema where elevated levels have been found compared to healthy volunteers and ARDS patients [39]. By utilizing highly sensitive RT-PCR techniques the amplification of SP-A transcripts can be used for the detection of occult metastases in non small cell lung cancer patients [5, 40] . Comparative studies of different malignomas with pulmonary localization have shown the diagnostic properties of immunohistochemically determined SP-A [6, 41, 42] . In carcinomas of occult origin localized in the lungs the diagnosis has a crucial influence on the therapy. A positive detection of SP-A represents a clear hint for a primary location in the lung [43]. Fig. 2 as an example shows the immunohistochemical detection of SP-A in a moderately differentiated adenocarcinoma of the lung using the primary monoclonal antibody PE-10 and LSAB (AEC-substrate, × 100). The positive staining in the tumor cells (reddish) in this certain case helped to manifest the diagnosis as a primary carcinoma of the lung.