The origin(s), differentiation and renewal of mucous cells during regeneration following traumatic injury and the origin(s) of mucous goblet cells which arise after intratracheal instillation of elastase will be characterized in hamster tracheal epithelium. Regeneration will also be studied in abnormal tracheal epithelium (mucous goblet cell metaplasia and/or hyperplasia) and the process will be compared with the regenerative response of previously normal epithelium. Morphological (high resolution light microscopy and electron microscopy) autoradiographical and histochemical techniques will be used to quantitate the respective roles played by basal cells and mucous cells during epithelial regeneration. Mucous cells, although differentiated, divide to produce daughter cells during the regenerative process similar to the situation in liver and kidney where differentiated parenchymal cells divide when required for regeneration following lethal cell injury. The genealogy of all cells which arise during regeneration will be characterized and quantitated using a computer operated vertical illumination microspectrophotometer. Proof that undifferentiated "indifferent cells" arise at the luminal surface of the epithelium prior to reestablishment of normal architecture, will be sought.