Ultrasound considerably enhances and simplifies photochemical reaction of cyclohexanone with cyclohexene. The Paterno-Büchi reaction of acetone with ethyl vinyl ether is enhanced by ultrasound and yields a different ratio of cis/trans oxetanes under sonication by comparison with the silent reaction. Sonication appears to affect the first reaction by homogenization of excited intermediates and by quenching the excited triplet state at the second reaction.