In order to better understand the pathogenesis of radiation-induced pulmonary fibrosis, techniques were developed to identify and quantitate connective tissue components of canine lung in the normal and diseased state. Lung tissue hydrolysates from normal dogs were prepared and amino acids were quantitated by chromatographic elution using a modified amino acid analyzer and mechanical integration. These methods yielded good resolution and acceptable integration of (a) hydroxyproline and hydroxylysine, indicators of collagen, and (b) desmosine, the indicator of elastin. The ability to measure hydroxyproline, hydroxylysine, and desmosine and thus obtain a quantitative estimation of the connective tissue content of normal canine lung lends confidence to the use of the technique reported here for measuring increased levels of connective tissue associated with pulmonary fibrosis.