Ultrasound was shown to enhance pretreatment of lignocellulose for biofuel and biorefinery applications and can augment oxidative processes, yet few studies have combined ultrasound with an oxidative environment for the pretreatment of lignocellulose. In the present contribution, pretreatment of a wheat straw using a combination of ultrasound with two oxidative pretreatments, peracetic acid and hydrogen peroxide, as well as water and acetic acid was tested. The experimentation was conducted in an ultrasonic-microwave reactor with a comparison to silent pretreatment with microwave heating alone. In addition, thermal heating was compared to microwave heating for the water pretreatment. Ultrasound produced a higher purity solid residue for all chemical pretreatments. However, ultrasound pretreatment reduced the delignification efficacy by up to 50%, attributed to lignin condensation. The chemical treatments were affected by sonolysis reactions and altered the recoverability of the solubilized carbohydrates. © 2013 American Chemical Society.