A comparison between the analytical performance of a hanging mercury drop electrode (HMDE) and a boron-doped diamond (BDD) electrode for the quantification of 4-nitrophenol (4-NP) in spiked pure and natural waters is reported in this work. Square wave voltammetry (SWV) was chosen as the electroanalytical technique and Britton-Robinson buffer as the electrolyte. For the reduction process, the quantification limits varied between 5.7 and 66.0 mugl(-1) for the HMDE and between 14.1 and 61.3 mugl(-1) for the BDD electrode for water samples with increasing degree of contamination. The oxidation of 4-NP on BDD was also used for analytical purposes and the quantification limits in this case varied from 9.4 to 53.1 mugl(-1). In all cases, the detection limits followed the same trend. These latter results illustrate the advantages arising from the possibility of using an oxidation process on BDD electrodes for analytical purposes in contaminated matrices. The recovery experiments showed values above 95% for spiked samples thus indicating the feasibility of the electroanalytical methodology to quantify 4-NP in pure or natural waters. HPLC measurements were also performed for comparison and confirmed the values measured by SWV. (C) 2004 Elsevier B.V. All rights reserved.