Some biologically important indolylthiohydantoin derivatives were investigated electroanalytically by voltammetric determination. Based on this study, a simple, rapid, sensitive and validated voltammetric method was developed for the determination of the indolylthiohydantoin derivatives that are readily oxidized at carbon-based electrodes. Due to the similarity between electrochemical and biological reactions it can be assumed that the oxidation mechanisms taking place at the electrode and in the body share similar principles. The oxidative behavior of the indole derivatives was studied as a function of pH at a glassy carbon electrode in different buffer media. The characteristics of the corresponding electrode reaction were discussed. The studied molecules are extensively metabolized in vivo, mainly through oxidative processes and we assume that the oxidation of the indolic compounds occurs on the nitrogen atom in the indole ring of the molecule. A linear response was obtained in the different media for all the compounds with a detection limit of 1.96x10(-6) M, 2.32x10(-6) M, 1.44x10(-6) M and 7.10x10(-7) M for compounds 1, 2, 3 and 4 respectively.