Few dissidents now dispute the contention that alveolar type II cells synthesize and secrete surface-active material (surfactant) in the lung. Autoradiographic (1), biochemical (2), developmental (3), and physical (2) studies now provide evidence that surface-active lipids and enzymatically active proteins are packaged and stored intracellularly as membrane-bound secretory granules, the lamellar bodies. Although these general concepts are supported by much experimental evidence, many questions remain unanswered concerning more intimate details of the synthetic processes that lead to lamellar body formation. For example, we do not know the site of synthesis of dipalmitoyl phosphatidylcholine, the major surface-active lipid of surfaceactive material, nor do we know the mechanism of assembly of the combined lipid-protein secretory product. We do not know whether the specific, nonserum proteins associated with surface-active material as characterized biochemically (4) are present within and are secreted with lamellar bodies. Similarly, we do not understand in detail the mechanisms by which an active surface film is generated from the chemically complex material secreted as a granule. In light of the important physiologic function of the surface film, this last intriguing ques-