Ultrasonic processing of a water soluble polymer, polyacrylamide, is investigated and molecular weight evolution during ultrasonic degradation was monitored online by light scattering and viscometry. The resulting Data were compared to various theoretical models. Initially the scission was very rapid but as the limiting molecular weight was approached it slowed down. This slowing down was too pronounced to be described by a first order model. Only the Giz, Ovenall/Harrington/Madras and Tang models, adequately accounted for this slowing down and gave good fits to the data.