Introduction: The epithelial sodium channel (ENaC) plays a key role in sodium homeostasis in tetrapod vertebrates. Four ENaC subunits (α, β, γ, δ) form heterotrimeric αβγ- or δβγ-ENaCs. While the physiology of αβγ-ENaCs is well understood, the function of δβγ-ENaC is unknown. The SCNN1D gene coding for δ-ENaC is a pseudogene in mice/rats, limiting research on δ-ENaC physiology. We investigated whether δ-ENaC is generally absent across rodents or limited to specific suborders. Methods: The presence of potentially functional SCNN1D genes was assessed for all currently sequenced rodent genomes. Two-electrode voltage-clamp and single-channel patch-clamp electrophysiology were used to record transmembrane currents of human and guinea pig αβγ- and δβγ-ENaCs expressed in Xenopus oocytes. Sodium self-inhibition (SSI) and activation by extracellular protease (chymotrypsin, 2  mg/ml), two mechanisms controlling ENaC activity, were characterised as previously described (Wichmann et al. 2019). Data are reported as means ± standard error, ‘n’ indicates the number of experiments. Results: While SCNN1D was lost in five rodent lineages, including Muridae (mice/rats), functional SCNN1D is present in species within 21 of 35 currently recognised rodent families. Fusion of SCNN1D exons 11 and 12 to a ‘super-exon’ was observed in the Hystricognathi, a suborder containing the Caviidae family (guinea pigs). The ‘super-exon’ causes intron DNA sequences to be translated into a structurally flexible part in the δ-ENaC extracellular domain. Whole-cell and single-channel electrophysiology revealed that guinea pig δβγ-ENaCs generate robust amiloride-sensitive currents. Amiloride-sensitive currents generated by guinea pig δβγ-ENaC (-6.03 ± 0.79 µA, n = 20) were significantly larger than those of αβγ-ENaC (-2.1 ± 0.21 µA, n = 19, p < 0.0001, Student’s unpaired t-test with Welch's correction), comparable to human ENaCs (δβγ-ENaC: -10.23 ± 3.25 µA, n = 10; αβγ-ENaC: -6.52 ± 3.19 µA, n = 10, p = 0.0191, Student’s unpaired t-test). The single channel conductance of guinea pig αβγ- and δβγ-ENaC were 4.43 ± 0.19 pS (n = 10) and 4.21 ± 0.35 pS (n = 7), respectively. In both species, the magnitude of SSI was greater in αβγ-ENaCs compared to δβγ-ENaCs (guinea pig αβγ-ENaC SSI: 46.52 ± 2.71 %, n = 18, guinea pig δβγ-ENaC SSI: 16.09 ± 2.49 %, n = 17, p < 0.0001, Student’s unpaired t-test; human αβγ-ENaC SSI: 57.68 ± 2.21 %, n = 10, human δβγ-ENaC SSI: 17.72 ± 0.99 %, n = 10, p < 0.0001, Mann-Whitney U-test). Extracellular chymotrypsin stimulated guinea pig αβγ-ENaC currents by 1.52 ± 0.08 fold (n = 13), but not δβγ-ENaC currents (0.78 ± 0.03 fold, n = 15, p < 0.0001, Mann-Whitney U-test). Similarly, human αβγ-ENaC currents increased 1.78 ± 0.11 fold (n = 9), but not δβγ-ENaC currents (1.13 ± 0.06 fold, n = 9, p = 0.0002, Student’s unpaired t-test with Welch's correction). Conclusion: δ-ENaC is not generally absent from rodents but was independently lost in five lineages. Guinea pigs have two functional αβγ- and δβγ-ENaC isoforms with biophysical and regulatory features similar to human orthologues. Guinea pigs represent a commercially available rodent model for studying mammalian δ-ENaC.