The cyclic voltammograms of amiloride at the hanging mercury drop electrode showed a single well-defined four-electron irreversible cathodic peak in Britton-Robinson (B-R) buffer of pH 2. At higher pH values (pH > or =3), two irreversible cathodic peaks corresponding to the transfer of four (first peak) and two (second peak) electrons, were obtained The peak potentials were shifted to more negative values on the increase of pH of the medium, implying the involvement of protons in the electrode reaction and that the proton-transfer reaction precedes the proper electrode process. The 4-electron single peak (pH 2) or the first peak (pH > or = 3) may be attributed to the cleavage of the -CH=NH double bond of the N-imidino amide group with the release of NH(3) molecule. While the second peak may be due to the saturation of the C?O double bond of the carboxamide moiety. Based on the interfacial adsorptive character of the drug onto the mercury electrode surface, a simple, sensitive and low cost square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure was optimized for analysis of the drug. The optimal operational conditions of the proposed procedure were: accumulation potential E(acc)= -0.7 V, accumulation time t(acc)= 60-65s, scan increment= 10 mV, pulse-amplitude = 50-60 mV, frequency =120 Hz using a B-R buffer of pH 8 as a supporting electrolyte. The linear concentration range was found to be 2 x 10(-9) to 2 x 10(-7) M amiloride with limits of detection (LOD) and quantitation (LOQ) of 1.9 x 10(-10) and 6.3 x 10(-10) M, respectively. The procedure was successfully applied for determination of amiloride in pharmaceutical formulation and spiked in human serum. The LOD and LOQ of amiloride spiked in human serum were 5.7 x 10(-10) and 1.9 x 10(-9) M amiloride, respectively. The procedure did not require sample pretreatment or any time-consuming extraction or evaporation steps, other than deproteinization and then centrifugal separation of protein from serum sample prior to analysis of the drug.