The efficiency of UV/H(2)O(2) treatment using KrCl (222 nm) and XeBr (282 nm) excilamps was examined for removal of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) from aqueous solution in the molecular form (pH 2 and un-adjusted pH) and anionic form (at pH 11). UV/H(2)O(2) treatment of 2- or 4-CP was initially carried out at un-adjusted pH with varying molar ratios of chlorophenol and H(2)O(2). The para-chlorobenzoic acid was used as a hydroxyl radical (•OH) probe compound. UV/H(2)O(2) treatment of 2- and 4-CP with a molar ratio of 1:25 at ambient pH and a fluence of 4.1 J/cm(2) provided a significant decrease in chemical oxygen demand (COD). Under these conditions, the •OH exposure was found to increase from 0.5 × 10(-11) and 0.4 × 10(-11) to 1.8 × 10(-11) and 1.3 × 10(-11) M min for KrCl and XeBr excilamp, respectively. Compared with direct UV photolysis, the pseudo-first-order fluence-based rate constants of 2- and 4-CP degradation in UV/H(2)O(2) process at a molar ratio of 1:25 were significantly higher for molecular 2-CP and 4-CP in the anionic form using both excilamps. Detailed information on UV fluence and/or the exposure to •OH radicals is proposed to accurately compare studies reporting the effectiveness of AOPs based on excilamps.