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Two procedures developed earlier by the authors for the spectrophotometric determination of hydroxyproline have been tested on hydrolysates of dried formalin-fixed and ethanol-fixed lung tissues. The effects of dilution of the hydrolysates and of the presence of various amounts of sodium chloride have been studied, as well as several methods commonly used t o remove competing amino-acids or other interfering materials from hydrolysates before the spectrophotometric determination of amino-acids. Several amino-acids reported to cause interference in other spectrophotometric methods for hydroxyproline determination have a negligible effect in the procedures used in the present study.Lung tissue hydrolysis with varying concentrations of hydrochloric acid, sulphuric acid and sodium hydroxide, under various conditions, has been studied. No reduction in hydroxyproline yield was observed when the acid hydrolyses were prolonged for several days. A simple procedure is described, in which hydrolysis takes place overnight a t 105" C in a polypropylene tube enclosed by a glass tube fitted with a spring-loaded stopper; this procedure has given good results over a long period.

The amino acid contents of dust-affected coalworkers' lungs, complicated pneumoconiotic lesions, the remainder of the lungs from which the lesions had been removed and dust-free control lungs have been determined. The results have been corrected for blood, dust, fat and collagen content, but no significant differences between dust-free and dust-affected lungs were found. The residual amino acid results, after correction, closely resembled the results for glycoprotein extracted from human lung pleura and aorta.