The electropolymerization of indole-5-carboxylic acid leads to the deposition of a film on the electrode surface. Two different chemical species are deposited, and these can be separated by their differential solubility in dimethylformamide (DMF). These products have each been characterized by mass spectroscopy, UV-visible and fluorescence spectroscopy, IR spectroscopy and NMR spectroscopy. It is clear from these data that the DMF-soluble species is an electrodeposited trimer, whereas the species which is much less soluble in DMF or tetrahydrofuran, but is soluble in dimethylsulphoxide, appears to be a polymeric species made up of linked trimer units.