The production of indium-tin oxide has increased during the past decade, owing to the increased manufacture of liquid-crystal panels, especially in Japan. We carried out a medical checkup including high resolution CT (HRCT), pulmonary function test, KL-6, SP-D and serum indium concentration, for 40 men (mean age 40.4 +/- 12.4 years old) working in an indium plant. Four workers who were all smokers had emphysematous changes on HRCT and one subject (non-smoker) had lung cancer. There were no findings of interstitial changes on HRCT. Serum KL-6 was significantly elevated (over 500U/ml) in 9 subjects (22.5%). Subjects with a high concentration of serum indium (3ng/ml<) had significantly longer exposure periods, higher KL-6 and SP-D levels compared with those with a low concentration (3ng/ml>). The serum indium concentration positively correlated with the KL-6 level. These results suggest that inhaled indium compounds can cause pulmonary disorders such as interstitial changes.