Cyclic voltammetry studies were carried out on a platinum electrode in alkaline 1 M NaOH solutions containing 0.1 M of phenol, monochlorophenols, dichlorophenols, trichlorophenols and pentachlorophenol in order to compare their electropolymerization ability and the degree of deactivation of the electrode. These show that fouling of the Pt electrode occurs during the electrooxidation of all the phenols studied. Almost full deactivation of the electrode occurs in the case of phenol and 3-chlorophenol after five cycles, while 4-chlorophenol, 3,4-dichlorophenol, 2,4-dichlorophenol and 2,4,5-trichlorophenol deactivate the electrode completely after the first cycle. Partial deactivation of the electrode occurs in the case of 2-chlorophenol, 2,3-dichlorophenol, 2,6-dichlorophenol, 2,5-dichlorophenol and 2,4,6-trichlorophenol. A weak fouling of the electrode occurs in the case of 3,5-dichlorophenol, 2,3,6-trichlorophenol and pentachlorophenol. Such differences in the degree of electrode deactivation may be explained by the different structure (permeability) of the polymeric tars formed. The structure of the tars depends on the monomer structure. Presumably, more regular and dense polymer structures deactivate the electrode more rapidly. More branched, irregular high molecular weight substances deactivate the electrode more slowly.