Tricomplex flocculation has been used to visualize pulmonary surfactant phospholipid in the light microscope in a similar manner to its original application as a staining method for spots of phospholipid on chromatographic paper. Fixation of lung and staining of surfactant are performed in one operation by combining glutaraldehyde with the tricomplex reagents. The staining solution is composed of appropriate amounts of acid fuchsin, uranyl nitrate, and 0.1N hydrochloride in water. After glutaraldehyde-tricomplex treatment, sections of human and rat lungs examined with phase optics show a blue layer of material lining epithelial surfaces of alveoli and similar material within type II alveolar cells. It is believed that this material represents the alveolar surface layer of surfactant phospholipid and the sites of synthesis and storage of this material within alveolar type II cells.