A sensitive electrochemical procedure based on ds-DNA interaction with amiloride at a ds-DNA-modified pencil graphite electrode (PGE) was introduced as a promising tool for determination of amiloride. An adsorptive stripping voltammetry was applied for the immobilization of ds-DNA on PGE in acetate buffer (pH 4.8). Differential pulse voltammetry (DPV) was carried out to obtain the change in the oxidation signal intensity of guanine and adenine before and after interaction with amiloride. The decrease in intensity of the guanine and adenine oxidation signals was used as an indicator for the sensitive determination of amiloride. Under the optimum conditions, a linear dependence of the guanine and adenine oxidation signals was observed to the amiloride concentration in the range of 0.75-240 mu mol L-1 with a detection limit of 0.5 mu mol L-1. The relative standard deviations of 10 replicate measurements of 1.0 and 10.0 mu mol L-1 amiloride concentrations were 4.7% and 5.3%, respectively. UV-vis measurements combined with DPV were also carried out to propose the most Plausible mechanism for the interaction of amiloride and dsDNA. The influence of potential interfering substances on the amiloride determination was studied. Finally, the ds-DNA-modified PGE biosensor was applied for the determination of amiloride in tablets and urine samples with satisfactory results. (C) 2008 Elsevier Ltd. All rights reserved.