A web site presents a graph–like spatial structure composed of pages connected by hyperlinks. This structure may represent an environment in which situated agents associated to visitors of the web site are positioned and moved in order to monitor their navigation. This paper presents a heterogeneous multiagent system supporting the collection of information related to user’s behaviour in a web site by specific situated reactive user agents. The acquired information is then exploited by interface agents supporting advanced adaptive functionalities based on the history of user’s movement in the web site environment.