Elastin from anatomically defined regions of young calf lung and dog aorta was isolated and purified by a procedure which sequentially removed lipids, collagen, structural glycoproteins, and the microfibrillar proteins without apparent damage to the cross-linking residues, which have been shown to be sensitive to autoclaving and hot alkali treatment. One of the methods described was effective in obtaining pure elastin from lung parenchyma. Visceral pleura was found to be the richest source (25% dry weight) of elastin in the lung tissues examined. The amino acid compositions of the elastins purified by different methods were compared for purity and for the detection of possible damage to cross-linking compounds. Cross-linking profiles were obtained by column chromatography either after reduction with 3[H]NaBH4 or after reaction with 14[C]NaCN and NH3. The 3[H]NaBH4 method, under carefully controlled conditions, proved not to be quantitatively reproducible. The reaction of elastin with 14[C]NaCN and NH3 appeared preferable due to its reproducibility; this procedure required one type of hydrolysis for the analysis of all the cross-linking compounds. Examination of the cross-linking profiles of the elastins from various tissue regions revealed differences in the type, distribution, and quality of cross-links.