Potassium hydroxide (KOH) preparations for elastin fibers on sputum obtained from 80 patients seen over a four-month period at two Cleveland hospitals were performed. The results were compared with roentgenographic evidence of necrosis and case diagnosis. Sixty-one patients had neither elastin in sputum nor roentgenographic evidence of cavitation; 11 had positive results using both methods. Two patients had no elastin fibers in sputum but had parenchymal pulmonary cavities on chest x-ray film. Six patients had elastin observed in KOH preparations of sputum, but no cavitation roentgenographically. The presence of elastin in sputum was strongly correlated with roentgenographic evidence of pulmonary necrosis (p = 5.7 X 10(-8]. Including patients seen before, after, and during the prospective study, we have observed a total of nine with positive sputum preparations for elastin and no cavitation on chest x-ray film for whom tissue was available for study. All had pulmonary necrosis histologically. Our observations suggest that the KOH preparation of sputum for elastin fibers may be more sensitive than the chest roentgenogram in the detection of pulmonary necrosis and may be a useful adjunct in the diagnosis of necrotizing disease.