An electroneutral Na⁺/H⁺ exchange mechanism (dimethylamiloride inhibitable, Li⁺ sensitive, and Ca²⁺ insensitive) was identified in brush-border membrane vesicles (BBMV) from Kuruma prawn hepatopancreas by monitoring Na⁺-dependent H⁺ fluxes with the pH-sensitive dye acridine orange and measuring ²²Na⁺ uptake. Kinetic parameters measured under short-circuited conditions were the Na⁺ concentration that yielded one-half of the maximal dissipation rate (F_max) of the preset transmembrane pH (K_Na) = 15 ± 2 mM and F_max = 3,626 ± 197 F · min¹ · mg protein¹, with a Hill coefficient for Na⁺ of ~1. In addition, the inhibitory constant for dimethylamiloride was found to be ~1 µM. The electroneutral nature of the antiporter was assessed in that an inside-negative transmembrane electrical potential neither affected kinetic parameters nor stimulated pH-dependent (intracellular pH > extracellular pH) ²²Na⁺ uptake. In contrast, electrogenic pH-dependent ²²Na⁺ uptake was observed in lobster hepatopancreatic BBMV. Substitution of chloride with gluconate resulted in increasing K_Na and decreasing F_max, which suggests a possible role of chloride in the operational mechanism of the antiporter. These results indicate that a Na⁺/H⁺ exchanger, resembling the electroneutral Na⁺/H⁺ antiporter model, is present in hepatopancreatic BBMV from the Kuruma prawn Penaeus japonicus.