A bismuth-film electrode for use in cathodic electrochemical detection was employed in order to quantify sulfadiazine in pharmaceutical formulations. The bismuth film was deposited ex situ onto a glassy carbon substrate. Analysis of two sulfa drugs was carried out by differential-pulse voltammetry in 0.05 mol L-1 Britton-Robinson pH 4.5 solution. Sulfadiazine reduction was observed at -0.74V vs. Ag/AgCl in one well-resolved irreversible reduction peak. The analytical curve with two slopes was obtained in the concentration range of 3.2-97.0 mu mol L-1. The detection limit was 2.1 mu mol L-1 for concentrations of 3.2-20.0 mu mol L-1 (r = 0.9949) and 12.2 mu mol L-1 for concentrations between 20.0 and 97.0 mu mol L-1 (r = 0.9951). Recovery studies carried out with both sulfadiazine samples gave values from 93.6 to 109.3%. The accuracy of the results supplied by the bismuth-film electrode was compared to those obtained by the standard amperometric titration method. The relative error between them was lower than 2.0%. (C) 2010 Elsevier Ltd. All rights reserved.