Kir7.1 K+ channel, encoded by the Kcnj13 gene, is a member of the inwardly-rectifying Kir family of proteins expressed in epithelia such as the choroid plexus, retina and small intestine. Owing to its remarkable colocalisation with the Na+/K+-ATPase, Kir7.1 has been proposed to be responsible for K+ recycling needed to maintain high rates of ion and fluid transport across these epithelia. To study its role, we generated a Kcnj13-/- knockout (KO) mouse for Kir7.1 expressing the LacZ gene under the control of Kcnj13 promoter. Heterozygous (Het) mice were indistinguishable from their wild type (WT) littermates, but KOs presented growth retardation, craniofacial abnormalities, and did not survive beyond the first day of life (P0) (Villanueva et al., 2015). We detected Kir7.1 expression in the respiratory tree indirectly through β-galactosidase activity in cryopreserved sections. Tissues were obtained from adult mice euthanized with an overdose of Aventin (240 mg/Kg) or embryos and neonates sacrificed by cervical dislocation. Expression started at day 14.5 of gestation (E14.5) in the bronchi and progressed through the airways to reach the alveoli and pulmonary parenchyma at E18.5. Expression was also evident in adult Het respiratory system. Morphometric analysis of hematoxylin and eosin stained sections showed that P0 KO lungs had a lower air space at terminal sacs when compared with WT and Het mice (WT 58% ± 3.7%, n=13; Het 56% ± 1.1%, n= 25; KO 43% ± 1.8%, n=11; means ± SEM). Lungs of KO mice (measured at E18.5) also had thicker walls and lower content of fluid (WT 38% ± 6.1%, n=6; Het 40% ± 1.5%, n=15; KO 28% ± 2.8%, n=5). To assess the distribution of Kir7.1 protein we used the CRISPR-Cas9 technology to generate a knockin mouse where the native Kir7.1 protein was replaced by a haemagglutinin-Kir7.1 (HA-Kir7.1) fusion protein, allowing us to determine the subcellular localization of the Kir7.1 channel in the respiratory system. To corroborate that the addition of HA tag to the extracellular loop of the protein did not affect the subcellular localization of Kir7.1, we immunodetected the knocked-in channel with an anti-HA antibody in choroid plexus of HA-Kir7.1+/- adult mice. As expected, HA-Kir7.1 was present at the apical membrane of choroid plexus epithelial cells thus confirming previous results. Immunodetection experiments in the airways showed that Kir7.1 channel is expressed in the basolateral side of the epithelial cells of the trachea, bronchi and bronchioles, and in type II pneumocytes of the lungs of adult mice. We hypothesise that Kir7.1 channel is necessary for proper lung development in mice possibly playing a role in the adequate production of lung fluid, one of the main signals for lung maturation. In adult mice Kir7.1 may be relevant in airway and alveolar ion homeostasis.