Models of the lung airways of a rat were developed from complete measurements of the tracheobronchial airways. A silicone rubber cast of the tracheobronchial airways of a rat lung was prepared and all individual airway segments down to and including the terminal bronchioles were measured to obtain the segment diameters, lengths, branching angles and angles of inclination to gravity. Models of the rat tracheobronchial airways were constructed based on the original measurements and the subsequent analysis. Some mathematical assumptions about acinar anatomy distal to terminal bronchioles were made to extend the models to include pulmonary regions. Emphasis was placed on the "Typical Path Lung Model" which used one typical pathway to represent either a whole lung or a lobe of the lung. The models are simple and can be applied in calculation of physiologic variables or particle deposition during inhalation in various lobes of the lung.