Editor—In response to the commentary by Professor Walters,1 we must first correct him in referring to our model for the normal alveolus2 as “dry” when, in fact, it is based on many classic morphological studies3 4demonstrating fluid largely confined to “pools” at the septal corners. In proposing that an oligolamellar lining of surface–active phospholipid (SAPL) adsorbed to epithelium “pushes water aside” from the gas–exchange surface, we agree that it is difficult to prove direct binding conclusively. However, any intervening aqueous layer is no more than that normally sandwiched between adjacent planes of polar groups in such structures (fig 1). Moreover, this physiological milieu contains mobile cations which …