Surfactant Protein A (SP-A) is considered to be one of important host defence components against respiratory allergens and pathogens. SP-A has been suggested to play an anti-inflammatory role but under some circumstances also proinflammatory roles in the lung. Changes in the SP-A production in the lung or its baseline concentrations in the blood might be associated with progression or mortality at idiopatic pulmonary fibrosis (IPF). Reduced levels of SP-A in alveolar fluid were reported in other pulmonary diseases, e.g. acute respiratory distress syndrome (ARDS). Elevated levels of SP-A in lungs have been observed in pulmonary alveolar proteinosis (PAP). The Human SP-A ELISA kit is a sandwich ELISA intended for the determination of SP-A in human serum, plasma (heparin, citrate) and amniotic fluid. Purified human SP-A is used as a calibrator and was used to raise highly specific polyclonal antibodies employed in the assay.