PVP solutions were sonicated with high-intensity ultrasound, and the weight-average molecular weight was monitored by an ACOMP system. The use of continuous on-line data to critically evaluate various models showed that the molecular weight decreased towards a limiting value. Theoretical and phenomenological models of evolution of the molecular weight during sonication are compared with the on-line data. The Ovenall/Harrington/ Madras and Giz and Tang models werer found to describe the results adequately. These models share the property of an initial rapid drop in molecular weight followed by a slowing down of the rate of molecular weight decrease.