This article is the fifth in a series of articles from our study examining information-seeking behavior in relation to information-retrieval (IR) interaction. This article focuses on the examination of the interaction variables within Saracevic's () triadic IR model. The analysis involved an examination of the information-searching behavior of academic researchers during a mediated interaction with an IR system, particularly concentrating on the interaction between the information seeker, the search intermediary, and the IR system. To explore the variables during mediated search interaction, two small-scale studies of mediated on-line searching were conducted at the University of Sheffield. The studies involved mainly qualitative data analysis of interview transcripts and on-line search results, together with quantitative data analysis of questionnaire results. The studies specifically investigated: (1) aspects of the mediated search process, (2) relevant information sources, and (3) interaction measures derived from search logs and tape transcripts, and related interaction measures. Findings include: (1) a number of different types of interactions were identified, (2) the presearching interactions between information seeker and intermediary aided the information seeker to identify their idea and problem, and (3) most information seekers in this study were at the problem definition stage or problem resolution stage following the search process. From this research, it is clear that the interaction did affect the search process. The intermediary helped the users to identify their search terms more clearly and focus on the references obtained. In most cases, the users and intermediary considered the communication process very effective, and the interactions that took place during the on-line search were found to affect the users' perceptions of the problem, personal knowledge, and relevance judgments. The interaction process aided the users to obtain very useful results with help from the intermediary. In general, the users gave a positive evaluation of the retrieved answers in terms of focus, completeness, novelty, and degree of nonrelevancy.