Electrochemical oxidation of 4-hydroxyindole has been studied at pyrolytic graphite electrode in aqueous phsophate buffers of pH 2.1–10.1. Oxidation has been found to proceed in a single well-defined peak. The number of electrons involved under CV conditions were found as 1.3 ± 0.1 and were different than CPE (2.7 ± 0.2). The spectral studies during oxidation indicated that no UV-absorbing intermediate is generated in the reaction. The products of oxidation were separated by HPLC and characterized by m.p., 1 H NMR, and mass spectra as a hydroxy tetramer. A single dose of the oxidation product at LD 50 value on intracranial injection in albino mice produced substantial changes in blood parameters and indicated liver disorder and hyperthyroidism conditions.