[en] Background: Diagnosis of canine idiopathic pulmonary fibrosis (IPF) is challenging. Endothelin-1 (ET1) is a biomarker of IPF in humans, but whether ET1 can detect and differentiate IPF from other canine respiratory diseases is unknown. Objective: To evaluate whether measurement of the concentration of ET1 in serum and bronchoalveolar lavage fluid (BALF) can be used to distinguish canine IPF from chronic bronchitis (CB) and eosinophilic bronchopneumopathy (EBP). Animals: Twelve dogs with IPF, 10 dogs with CB, 6 dogs with EBP, 13 privately owned healthy West Highland White Terriers (WHWT), and 9 healthy Beagle dogs. Methods: Prospective, case control study. ET1 concentration was determined by ELISA in serum and in BALF. Results: No significant difference in serum ET1 concentration was detected between healthy Beagle dogs and WHWT. Serum ET1 concentration was higher in dogs with IPF (median interquartile range; 2.32 pg/mL, 2.05-3.38) than healthy Beagle dogs (1.28, 1.07-1.53; P < .001), healthy WHWT (1.56, 1.25-1.85; P < .001), dogs with EBP (0.94 0.68-1.01; P = .001), and dogs with CB (1.54 0.74-1.82; P = .005). BALF ET1 concentration was below the detection limit in healthy WHWT and in dogs with CB, whereas it was measurable in all dogs with IPF. A cut-off serum concentration of 1.8 pg/mL had a sensitivity of 100% and a specificity of 81.2% for detection of IPF, with an area under the receiver operating characteristic curve of 0.818. Conclusions and Clinical Importance: Serum ET1 can differentiate dogs with IPF from dogs with EBP or CB. ET1 can be detected in BALF of dogs with IPF.