The stability of human lungs depends on a complex mixture of lipids and proteins called the pulmonary surfactant. This surfactant layer reduces surface tension of the alveolar fluid and avoids alveolar collapse. Although the functions of the pulmonary surfactant are relatively well known, its exact components are not as well characterized. It is important to characterize these components in order to understand surfactant alterations in a diseased state and its interactions with foreign materials. The goal of this study was to measure the amounts of phospholipids and proteins of Infasurf, a natural lung surfactant extracted from calf lungs. The total protein content of the surfactant was quantified using the bicinchoninic acid (BCA) assay. This assay provides a colorimetric detection when available proteins chelate BCA with cuprous ions to form a dark purple complex that can be measured at 562 nm. Total phospholipid measurements were performed using the ascorbic acid method. This method measures the total phosphorus amount of Infasurf, from which the amount of phospholipids can be estimated. It is based on the reaction between ascorbic acid and phosphomolybdate complex, which results in the reduction of the phosphomolybdate complex and gives a measurable absorbance at 820 nm. We found the protein and phospholipid content of Infasurf to be 0.7 mg/ml ± 0.09 mg/ml and 12.8 ± 0.514 mg/ml, respectively. The value for the total protein component is in agreement with the estimations of previous studies, while the phospholipids quantification is lower than what has been previously reported in other studies. Further studies are underway to determine the phospholipids and proteins of the Infasurf after exposure to carboxyl modified polystyrene nanoparticles (200 nm)."