The effects of methanol and carbon tetrachloride (CT) on the degradation of 1,4-dioxane via ultrasound irradiation were investigated by estimating the production rate of H2O2 and the degradation efficiency of the substrates. At 5 and 20 degrees C, the production rate of H2O2 significantly decreased as methanol concentration in pure water increased and during sonolysis of 1,4-dixoane. The sonolytic efficiency of 1,4-dioxane with methanol greatly decreased over 60 min at 5 degrees C and 90 min at 20 degrees C. Production of H2O2 increased during CT sonolysis at 5 degrees C but decreased at 20 and 40 degrees C, with efficiency greatest at 5 degrees C. Sonolysis of 1,4-dioxane with CT was enhanced from the beginning reaction at 5 degrees C and 40 min at 20 degrees C compared to the reactions without CT but was slightly lower at 40 degrees C. The results elucidate sonolytic mechanisms, such as pyrolysis and redox, in relation to reaction temperature, as well as suggest sonolytic conditions for the effective degradation of CT and 1,4-dioxane.