We used technetium-99m hexamethylpropylene amine oxime (Tc-99m HMPAO) lung scan to detect subclinical lung injury in patients with chronic renal failure (CRF), on regular hemodialysis (HD), who had normal chest X-ray findings (CXR) and pulmonary function test (PFT). The degree of pulmonary vascular endothelium damage was represented as lung/liver uptake ratios (L/L ratios) calculated by Tc-99m HMPAO lung scan. The L/L ratios of the 20 male CRF patients on HD with normal CXR and PFT were compared with those of the 20 male normal controls. The results show that the L/L ratios on Tc-99m HMPAO lung scans were significantly higher in CRF patients on HD (1.06 +/- 0.55) than those in normal controls (0.34 +/- 0.09). Using a cut-off value of 0.50, 18/20 [90%] CRF patients had abnormally increased L/L ratios. Our findings concluded that the pulmonary vascular endothelium damage represented as significantly increased L/L ratios on Tc-99m HMPAO lung scan in CRF patients on HD with normal CXR and PFT. In addition, Tc-99m HMPAO lung scan has the potential to be a sensitive, objective and noninvasive method to detect subclinical lung injury of CRF patients on HD, which is different from the traditional studies such as CXR or PFT.