This paper reports a study on the relationships between work tasks and users' performance when they interact with information systems, that is, interaction performance. An experiment with 24 participants was conducted to explore the issue. The participants were asked to search for useful information to support the completion of six simulated work task situations from operational information systems. Users' interaction performance is measured based on users' search effectiveness and efficiency. The results indicate: 1) Work tasks and time sufficiency for the search dramatically affect users' interaction performance. 2) Information sufficiency affects users' perception of their interaction performance. 3) The two facet of work tasks, i.e. product and objective work task complexity, significantly and interactively affect users' interaction performance to different degrees. 4) In contrast to product, objective work task complexity is more influential on users' interaction performance. 5) In addition, the study identifies some indicators of work task characteristics, for example, the number of items users select to support their work tasks and the search time they spend in locating useful information for a work task. The results shed light on the role of work task in information search and retrieval. The findings help improve interactive information systems design and personalization of information retrieval.