Objective. The purpose of this study was to evaluate the effect of three different irrigating solutions (17% EDTA, 10% citric acid and 2.5% NaOCl) and KTP laser irradiation on apical leakage using an electrochemical method. Materials and methods. Sixty extracted single-rooted human teeth with mature apices were instrumented up to a size 35 K-file. After using each file and before proceeding to the next, canals were irrigated with 2 ml of 2.5% NaOCl. All teeth were then randomly divided into four groups. In group 1, the root canals were irrigated with a final flush of 17% EDTA. In group 2, the root canals were irrigated with a final flush of 10% citric acid. In group 3, the root canals were irradiated with KTP laser at 1W, 4.45 J/cm(2). In group 4, the root canals were irrigated with a final flush of 2.5% NaOCl. The root canals were then filled using the cold lateral condensation method. Apical leakage was evaluated using an electrochemical method over a period of 10 days. Data were analysed using Tukey HSD and Friedmann tests with p = 0.05 as the level for statistical significance. Results. The 17% EDTA and 10% citric acid groups had statistically less apical leakage than the 2.5% NaOCl group at days 7, 8, 9 and 10 (p < 0.05); however, no significant differences were found between the tested groups at the other time intervals (p > 0.05). No significant difference was found between the KTP laser group and other groups tested at all time intervals (p > 0.05). Conclusion. All groups were unable to eliminate apical leakage. However, final irrigation with 17% EDTA and 10% citric acid following root canal preparation reduced postobturation apical leakage compared with 2.5% NaOCl irrigation. When KTP laser and the other three irrigants were compared, no siginificant difference was found.