Pulmonary surfactant is essential for normal lung function because it prevents alveolar collapse at low lung volumes. Pulmonary surfactant protein A (SP-A) is a component of pulmonary surfactant and plays a role in surfactant biology and in the innate host defense and regulation of inflammatory processes. SP-A has four structural domains: a cysteine-containing amino terminus, a collagenlike domain, a neck region, and a carbohydrate recognition domain. These domains of the SP-A molecule are involved in different aspects of SP-A function. Primates have two functional genes of SP-A, SP-A1 and SP-A2. The significance of these two similar genes is not known, but the patterns of their expression could differ. These genes are also differentially regulated during development. The complexity of the SP-A system at the molecular level reflects quantitative and qualitative differences not only under normal circumstances but also in certain disease states. SP-A is a multimeric molecule consisting of six trimers. Each trimer contains two SP-A1 molecules and one SP-A2 molecule. The size of human SP-A monomers ranges between 25 and 29 kDa, and the dimers between 48 and 60 kDa. We are purifying SP-A from porcine pulmonary extracts to provide it for important medicine research studies and/or therapeutics application. One clarified and acidified pulmonary extract sample after nonreducing and reducing SDS-PAGE presented only the expected bands corresponding to monomers and dimers observed in pure human SP-A. The Western blotting results with an antiserum to human SP-A showed the same recognition patterns even regarding some immunoreative bands with lower molecular mass observed in monomers and dimers of human SP-A attributed to different glycosilation patterns due to the molecular complexity of the genes expression. An analyzed bovine bronchoalveolar lavage sample had extra bands not recognized by the same antiserum to human SP-A. These results permit us to consider this sample as a promissory source of porcine SP-A.