1. Elastins were isolated from the visceral pleuras and parenchymas of lungs of humans of different ages. 2. The elastin content of pleuras increased whereas that of parenchymas remained constant with increasing age. 3. The amino acid compositions and carbohydrate contents of elastins isolated from both pulmonary tissues changed in the same way with increasing age of the subjects. These changes were similar to those observed in elastins isolated from the aorta. 4. Similar glycoproteins were isolated from pleuras and aortas, and were more difficult to extract from the elastins of older subjects. Contamination with these glycoproteins was responsible for the changes in composition of elastin, as the age of the tissue from which it was extracted increased. 5. The amount of the cross-linking amino acids desmosine and isodesmosine was lower in elastins isolated from both aorta and pulmonary tissues of senile subjects than those from younger subjects.
