Automated static analysis is a promising technique to detect defects in software. However, although considerable effort has been spent for developing sophisticated detection possibilities, the effectiveness and efficiency has not been treated in equal detail. This paper presents the results of two industrial case studies in which two tools based on bug patterns for Java are applied and evaluated. First, the economic implications of the tools are analysed. It is estimated that only 3–4 potential field defects need to be detected for the tools to be cost-efficient. Second, the capabilities of detecting field defects are investigated. No field defects have been found that could have been detected by the tools. Third, the identification of fault-prone classes based on the results of such tools is investigated and found to be possible. Finally, methodological consequences are derived from the results and experiences in order to improve the use of bug pattern tools in practice.