This paper presents an investigation of the self-serving biases of interface agent users. An experiment that involved 202 MS Office users demonstrated that, in contrast to the self-serving hypothesis in attribution theory, people do not always attribute the successful outcomes of human–agent interaction to themselves and negative results to interface agents. At the same time, it was found that as the degree of autonomy of MS Office interface agents increases, users tend to assign more negative attributions to agents under the condition of failure and more positive attributions under the condition of success. Overall, this research attempts to understand the behavior of interface agent users and presents several conclusions that may be of interest to human–computer interaction researchers and software designers working on the incorporation of interface agents in end-user systems. Ó 2006 Elsevier B.V. All rights reserved.