A square-wave voltammetry method for the determination of hydroxychloroquine (HCQ) in pharmaceutical and synthetic urine samples with a cathodically pretreated (CPT) boron-doped diamond (BDD) electrode was successfully developed. Using cyclic voltammetry, the HCQ oxidation was shown to be a one-electron diffusion-controlled process. The obtained SWVanalytical curve (I-pa/mu a = 0.033 + 1.24 [HCQ/mu mol L-1)]) for HCQ determination (using 0.1 mol L-1 H2SO4 as supporting electrolyte) presented a linear response from 0.1 to 1.9 mu mol L-1, with a detection limit of 0.06 mu mol L-1, the best value attained yet with an unmodified electrode. The proposed method was successfully applied in the determination of HCQ in pharmaceutical (tablets) samples, with results similar at a 95% confidence level to those obtained using a reference spectrophotometric method. Additionally, adequate recovery results were obtained for the determination of HCQ in doped synthetic urine samples. The novel proposed method is inexpensive and fast, with no need of sample pretreatment. (c) 2014 Elsevier B.V. All rights reserved.