This paper introduces rule-based exploratory testing, an approach to GUI testing that combines aspects of manual exploratory testing with rule-based test automation. This approach uses short, automated rules to increase the bug-detection capability of recorded exploratory test sessions. A preliminary evaluation found that this approach can be used to detect both general and application-specific bugs, but that rules for general bugs are easier to transfer between applications. Also, despite the advantages of keyword-based testing, it interferes with the transfer of rules between applications.