Purpose: We measured pulmonary epithelial permeability by Tc-DTPA radioaerosol clearance in patients with diabetes and correlated with the presence of microangiopathy to understand the pathophysiology of pulmonary microangiopathy and evaluate Tc-DTPA radioaerosol clearance as a diagnostic test to assess pulmonary microangiopathy. Materials and Methods: We performed ' Tc-DTPA radioaerosol scan in 10 normal subjects, 10 asym-ptomatic smokers, 20 diabetic patients without history of smoking (10 with microangiopathy, 10 without microangiopathy). Tc-DTPA clearance half-time (T1/2) was calculated, then compared with the result of chest radiography and pulmonary function test. Results: Chest radiography and pulmonary function test were normal in all subjects. There were no significant difference of clinical or laboratory characteristics between these groups except age. The diabetic patients with micraangiopathy were significantly older (p<0.05). The T1/2of normal subjects and asyrnptomatic smokers were significantly different (65.2+23.7min vs 39.6+9.8min, p<0.05). For diabetic patients with microangiopathy, the T, was 90 5+46.5min and significantly delayed when compared with those of normals and asymptomatic smokers (p<0.05). However, the T1/2of diabetic patients without microangiopathy, 70.0+12.7 min, was not significantly different from those of normals or asyrnptomatic smokers (p>0.05). No significant correlation was found between the T1/2and spirometric parameters including DLcc>, FVC, FEV>, FEV(/FVC (%) and FEF)5-75g in all subjects, and between the T1/2 and duration of diabetes in diabetic patients. Conclusion: Eventhough the influence of age cant be excluded, delayed " Tc-DTPA clearance half-time (T1/2)in diabetic patients with microangiopathy indicates decreased pulmonary cspillary permeability as one of the pathophysiologic results of pulmonary microangiopaththy. Further studies are needed in larger number of age matched control and diabetic patients to evaluate the diagnostic efficacy. (Korean J Nucl Med 1998;32:266-75)