Abstract HISTOLOGICAL examination of birds’ lungs indicates a considerable variation in air and blood volumes (Olander et al., 1967). However, in order to obtain quantitative estimates of these changes, methods are needed which can be applied to the entire organ. Such information is of importance in evaluating respiratory function in conditions where the lung becomes anatomically altered. Previous measurements of lung blood volumes in birds (Altman and Dittmer, 1961; McFarland, 1964) have not been made so as to prevent postmortem changes in blood volume in the organ. Other estimates of air volumes in the avian lung (King and Payne, 1958, 1962; Zeuthen, 1942) have been made by filling the respiratory tract with some foreign substance, the difficulties of which have been recognized. Consequently, new methods have been devised to measure air volumes (by buoyancy) and blood volumes (by isotope dilution) and these as well as data on normal chickens are reported . . .