An Ion-Interaction RP-IIR-HPLC method was developed, able to simultaneously separate neutral, basic, and acidic pesticides in a single run. The proposed method was validated by comparison of the results obtained for the same sample by conventional RP-HPLC and GC/MS methods. For this purpose parametrict-,F-,t-paired, and t- for multiple samplesand non parametricWilcoxon matched-pair signed-ranktests were employed. The accuracy of the proposed IIR-RP-HPLC method was evaluated with respect to a lab-made reference sample of spiked tap water.