This paper introduces an approach to web application regression testing, based upon repair of user session data. The approach is entirely automated. It consists of a white box examination of the structure of the changed web application to detect changes and a set of techniques to map these detected changes onto repair actions. The paper reports the results of experiments that explore both the performance and effectiveness of the approach. The effectiveness experiment uses an implementation of the repair algorithm applied to the online bookstore application over a series of 10 releases.