A rapid sensitive and versatile method for simultaneous determination of 2-mercaptobenzothiazole (MBT) and 2-mercaptobezoxazole (MBO) based on the square wave voltammetric, (SWV) using mercury drop electrode (SMDE) has been presented. A three-electrode system containing SMDE working electrode, Pt auxiliary electrode and Ag/AgCl reference electrode was used throughout. The linear calibration graphs are in the concentration range of 7-40 mu g mL(-1) and the equations are: (Delta i) = 1.372C(MBT) - 9.112 (r=0.9982) and (Delta i)=0.246C(MBO) - 1.736 (r=0.9985) for MBT and MBO, respectively. Partial least squares regression (PLS) was applied to resolve the seriously overlapped voltammograms without any pre-separation step. The five level partial factorial design was used as calibration design method and the cross-validation method was used to select the number of significant factor for PLS model building. Five significant PLS components are used for MBT and MBO. A set of synthetic sample mixtures were used to validate the propose method. The root-mean-square errors of predictions (RMSEPs) and percent of relative prediction errors (RPEs) are 0.841 and 0.777 mu g mL(-1) and 3.58 and 3.74% for MBT and MBO, respectively. The developed method was then applied to the analysis of these two compounds in different water samples with satisfactory results. (C) 2007 Elsevier B.V. All rights reserved.