This volume records the proceedings at the Fifth School of Thoracic Medicine held at the Ettore Majorana School of International Scientific Culture in March 1981. Foregathered there were a heterogeneous group comprising clinicians, pathologists, ultra-microscopists, biochemists, immunologists, cellular biologists and physiologists and they presented the twenty seven papers seen in the contents list. The discussion which followed each paper was faithfully recorded (and where necessary translated) and may be found after each author's presentation. This free discussion is perhaps the most valuable part of the School of Thoracic Medicine, and most clearly defines the present boundaries of knowledge, and the directions in which enquiry is being pursued. The collaboration of many people made the production of this book possible - for the translation and the discussion typescript Miss Guiliana de Ferio, for the final typing and layout Miss Corinne Wade ably assisted by Miss Karen Wadey and Miss Kim Lekstrom. The illustrations have been dealt with where necessary by Mr. John Griffiths and the production of the book was done at The Midhurst Medical Research Institute prior to its delivery to Plenum Press. CONTENTS The Innervation of Bronchial Mucosa • • • • • • • -. • • • • 1 Peter K. Jeffery Cell Division and Differentiation in Bronchial Epithelium • • • • • • • • • • • • • 33 Margaret Ayers and Peter K. Jeffery Cilia • 61 Bjorn A.