In patients with chronic renal failure, mechanical and hemodynamic changes could occur in the lungs without obvious pulmonary symptoms and findings and their effects could pave the way to pulmonary functional disorders. In this study, pulmonary functional disorders and especially alveolocapillary defects, which are frequently seen in uremia, were determined in renal transplanted patients. Pulmonary functions and diffusion capacity were assessed in uremic patients (n = 20) and in successfully transplanted patients (n = 20) without any lung disease or pulmonary edema symptoms and findings. Patients were selected randomly among outpatients who were followed up in a Nephrology and Transplantation Unit. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and peak expiratory flow (PEF25–75) were measured. Single breath carbon monoxide diffusion test and diffusion lung capacity adjusted for hemoglobin concentration (DLAdj) were done. The means of the spirometric values such as FVC, FEV1 and FEV1/FVC were normal in the nondialyzed uremic group, but the PEF25–75 value (68.7%) and diffusion capacity (DLAdj 72.7%) were found to be slightly low. There were 2 patients with normal values and 18 patients with some functional abnormalities in this nondialyzed uremic group. The means of all spirometric parameters and diffusion capacities were found to be normal in the transplanted group. There were 7 patients with normal function and 13 patients with some functional abnormalities in this transplanted group. When the nondialyzed uremic group and the transplanted group were compared statistically, significant differences were found between their spirometric values (except for FVC) and their diffusion capacities. Even though the uremic patients did not show any symptoms, their pulmonary function tests, especially diffusion capacity, were found to be disturbed. Although the transplanted patients as a group had normal mean spirometric values and diffusion capacity there were nevertheless many individual transplanted patients with defective diffusion capacity and abnormal spirometric values.