The alveolar integrity (AI) in 60 patients of noninsulin-dependent diabetes mellitus (NIDDM) who had normal chest X-ray findings and pulmonary function test was measured by technetium-99m (Tc-99m) diethyltriamine pentaacetic acid (DTPA) and Tc-99m hexamethylpropylen amine (HMPAO) radioaerosol inhalation lung scan (lung scan). The degree of AI damage in NIDDM was presented as the clearance rate (%/min) of hydrophilic Tc-99m DTPA and lipophilic Tc-99m HMPAO radioaerosols from the lungs. The AI of NIDDM patients was compared with the AI of 40 normal controls. The results show that (1) the clearance rate of Tc-99m DTPA radioaerosols was faster than those of Tc-99m HMPAO radioareosols in either NIDDM patients or normal controls over any portion of the lungs, (2) the clearance rates of both Tc-99m DTPA and Tc-99m HMPAO radioaerosols were faster in NIDDM patients than those in normal controls over any portion of the lungs. Our findings concluded that (1) at least two different clearance mechanisms of radioaerosols in the lungs are working; and (2) the AI damage in NIDDM patients happened in both hydrophilic and lipophilic parts of the alveoli. In addition, the AI damage found by faster clearance rates of both Tc-99m DTPA and HMPAO radioaerosols may provide the other objective evidence of lung complications in NIDDM patients, which are different from the traditional studies such as chest X-ray or pulmonary function test.