End-stage renal disease (ESRD) is a complex illness that involves different organs including the lungs. We studied the pulmonary function tests, arterial blood gases (ABG) and plasma endothelin-1 (ET-1) levels to check whether there is any change in their levels after hemodialysis (HD) in patients with ESRD. In this cross-sectional study (from July 2009 to April 2010), 20 patients with ESRD were evaluated. ABG, spirometric parameters and plasma ET-1 were measured before and after HD in these patients. Student's t-test was performed to clarify the differences and Pearson's test was used for correlations. P <0.05 was considered statistically significant. Significant reduction was seen in oxygen saturation (O₂sat), partial pressure of carbon-dioxide (PaCO₂) and oxygen (PaO₂) after a HD session (P <0.001). Also, improvement was seen in all spirometric parameters except forced expiratory volume (FEV1)/forced vital capacity (FVC) after HD. Plasma ET-1 levels decreased significantly after HD. Mean ET-1 before HD was 6.88 + 5.81 pg/mL while it was 3.91 + 2.76 pg/mL after HD (P = 0.009). Based on the plasma levels of ET-1, the patients were divided into two groups. The mean level of ET-1 was higher in the first group. Significant increase was seen in spirometric parameters in the second group. Our study suggests that, in patients with ESRD, plasma ET-1 level is higher than in the normal population, and this is closely related to deterioration of pulmonary function tests. Significant reduction of plasma ET-1 may be an important factor in the improvement of spiro-metry parameters after HD.