We present a new approach for performing load testing of web applications by simulating realistic user behaviour with stochastic form-oriented analysis models. Realism in the simulation of user behaviour is necessary in order to achieve valid testing results. In contrast to many other user models, web site navigation and time delay are modelled stochastically. The models can be constructed from sample data and can take into account effects of session history on user behaviour and the existence of different categories of users. The approach is implemented in an existing architecture modelling and performance evaluation tool and is integrated with existing methods for forward and reverse engineering.