The leech epithelial Na⁺ transporter (lENaT) has been thoroughly investigated. On the first sight, its properties seemed to be similar to the Na⁺ transport by epithelial Na⁺ channels (ENaC) in vertebrates, e.g. the amiloride sensitivity. Therefore, it was assumed that invertebrate lENaT and vertebrate ENaC could be identical. Meanwhile we found striking functional discrepancies, which allow contrary conclusions. We compared ENaC properties with those of lENaT by using electrophysiological and molecular biological techniques. Using modified Ussing-chambers we demonstrated that the protease trypsin had no effect on the Na⁺ transport across leech integument, while it increases Na⁺ transport in vertebrate ENaC. Additional differences were found in the regulation of Na⁺ absorption by H⁺ and Ni²⁺: While Ni²⁺ and pH = 4 decreased amiloride-sensitive currents in leech skin, both ions increase ENaC currents. For molecular studies we screened the cDNA library of Hirudo medicinalis with a specific ENaC antibody and carried out PCR approaches with a large number of degenerated ENaC primers, yet both approaches did not detect any ENaC-like protein. Therefore, we termed the putative leech Na⁺ transporter lENaT to clearly distinguish it from vertebrate epithelial Na⁺ channels.