The kinetics of the redox reaction between anti-hyperthyroid drug, propylthiouracil (PTU), and iodine was studied by cyclic voltammetry. Iodide is the mediator in the electrocatalytic oxidation of PTU at the surface of a platinum electrode. The second order rate constant (k(obs)) increased with pH in a pH range of 2 to 6. The reaction rate was also dependent on the concentration ratio of PTU to iodide. A simulation software was used to interpret the observations and to calculate k(obs) at different pHs. (C) 2013 The Electrochemical Society. All rights reserved.