To establish whether a correlation existed between emphysema and age, 24 lungs were used to measure the alveolar membrane fenestrations; the average area of 100 fenestrae was then plotted against age. Eighteen of these lungs were from patients 17 to 86 years of age with no history of respiratory ailments, whereas 6 lungs were from patients in whom an antemortem diagnosis of emphysema had been made. A significant, positive correlation between age and the area of fenestrae (t=2.4;p greater than 0.05) was found in the group of 18 lungs from patients with no respiratory ailements. The same could not be said categorically about the lungs from the emphysematous group, because the number of lungs examined was too small. We postulate that the pores of Kohn are part of the degenerating emphysematous process and are the first stage in the formation of fenestrae. A possible mechanism for the formation of fenestrae and their classification into 4 grades is presented.