In the final discussions of the last Ciba Symposium on Mucus and Mucosa (London, 1984), I voiced my impression that, in this gelatinous drama of mucus formation, several scripts were looking for characters, and some characters were looking for roles. Now, four years later, we have been able to locate a few of the missing characters and see them play their parts. Some, like the serous cell, are telling a potentially fascinating new story. A new polymer thread is being tentatively introduced into this already tangled scene of the mucus matrix (see review by Basbaum, this volume). Other cells, like goblet cells, are sticking to their old role of producing mucin, but are giving up some of their best-guarded secrets on how to store and release such gigantic molecules. We are also starting to realize that perhaps some charac ters can play not one, but several roles at the same time. For instance, mucous cells in vitro can not only produce mucin, but can also produce proteoglycans. Are we hearing the true scripts? Or is the culture shock, the isolation of these cells from their natural habitat, forcing them to play subsidiary roles? The whole picture of airway physiology is rapidly changing. Much remains to be learned, including perhaps the painful lesson that some of our most cherished passages in the old play are being swiftly rewritten. The mucosa of the airways is an organ. Its overall function results from the integrated action of several types of effector cells. Although the organ's