Quantitation of glycosaminoglycans (GAGs) in the lungs from different age groups indicated that the amount of GAGs was lower in the group 70 yr of age and older compared with that in the groups 30 to 39 and 40 to 49 yr of age, respectively (p less than 0.05). There was no difference in the relative ratio of individual GAG species (hyaluronic acid: chondroitin sulfate (A(C): dermatan sulfate: heparan sulfate) of the lung among the groups 40 to 49, 50 to 59, 60 to 69, and 70 or more yr of age. Hence, it was suggested that senescence of the lung was associated with a uniform decrease of all the GAG species in the lung. On the contrary, emphysematous lungs were characterized by a decrease in relative percentage of hyaluronic acid in comparison with control lungs (p less than 0.01).