Pulmonary complications are common in patients with chronic renal failure (CRF). The objective of this study was determination of the effect of renal transplantation on pulmonary function, using the methacholine challenge test. This was an interventional before after study. 14 patients with CRF on maintenance dialysis underwent serial spirometry and astography before and after renal transplantation. None of them was known to have clinically important pulmonary and heart diseases and the results of the spirometry, astography, echocardiography and CXR were normal .5 of the patients were male and all others were female. The age range was from 15-45 years (mean age = 28.6± 10.9). For every patient 4 times astography was done. The mean value of spirometric and astography indices before and after renal transplantation were within normal limit. But in statistic tests by repeated measure ANOVA, the results show improvement in airway responsiveness (although in normal limit).because the most common pathological condition of the lungs in CRF is pulmonary oedema, usually due to a combination of fluid overload and abnormal permeability of the pulmonary microcirculation, although our patients have no symptomatic pulmonary edema, minor degrees of fluid retention are virtually impossible to detect clinically and can not be excluded. So it seems that disappearance of sub clinical pulmonary edema is the likeliest cause of increase in Dmin and therefore improvement in airway responsiveness after renal transplantation.