The extracellular lining of the pulmonary peripheral airways is of vital importance to the lung. In this report, some aspects of the pulmonary extracellular lining and the epithelial cells believed to be responsible for its formation and secretion have been briefly reviewed. The influence of a number of toxic agents on the extracellular lining either directly or via those cells involved in its formation indicates that the extracellular lining may be important in understanding numerous toxic agent interactions with the lung. Images FIGURE 1. FIGURE 2. FIGURE 2. FIGURE 3. FIGURE 4.