The impact of different ultraviolet (UV) technologies combined with H2O2 irradiation on disinfection byproduct (DBP) formation was investigated using a broad range of UV doses. Four classes of DBPs (THMs, HAAs, aldehydes and carboxylic acids) were examined. This enabled the determination of effects resulting from the action of a UV-based Advanced Oxidation Technology (AOT; UV/H2O2 oxidation) on natural organic matter (aldehydes, carboxylic acids) as well as effects on the ultimate formation of chlorinated DBPs (THMs and HAAs) from secondary chlorination. For doses of less than 500 mJ/cm2, UV/H2O2 oxidation did not significantly affect THM and HAA formation in subsequent chlorination processes, however higher UV doses resulted in much lower ultimate concentrations of THMs and HAAs (approximately 50% lower). UV/H2O2 oxidation also resulted in the formation of aldehydes and carboxylic acids at UV doses above 500 mJ/cm2, compounds that are known to adversely effect drinking water biostability. Compared to UV irradiation alone at similar doses, UV/H2O2 oxidation had a more significant impact on DBP formation. Includes 24 references, table, figures.