The ultrasonic degradation of polybutadiene and isotactic polypropylene in solution was studied at different temperatures and in different solvents. The time evolution of molecular weight distribution was determined experimentally through gel permeation chromatography. Degradation rate coefficients were determined from a model based on continuous distribution kinetics and assuming mid-point chain scission. The variation of rate coefficients with vapour pressure and kinematic viscosity was also investigated. © 2004 Elsevier Ltd. All rights reserved.