The work presented here is aimed to guide environmental researchers and engineers in ultrasound-based chemical reaction systems, which are emerging as promising alternatives for the removal of refractory organics in treated effluents or natural waters. In accordance, the paper is presented in two parts as: (i) an extensive review of aqueous reaction systems catalyzed by ultrasonic pressure waves, with emphasis on basic theories, physical/chemical principles, state of the art, and figures-of-merits of sonochemistry, and (ii) a summary of lab-scale experimental work using ultrasonic reaction schemes for rendering or catalyzing the destructional removal of organic compounds by oxidation in the bulk liquid upon hydroxylation. and/or by thermal decomposition in the gaseous bubble. (C) 2001 Elsevier Science B.V. All rights reserved.