Marketing databases are currently one of the most important resources in any marketing departments. Regarding their customer knowledge needs many of them had develop their own database repository system. Although it immediate usefulness, as long as their databases were growing that behavior had revealed insufficient and created others barriers to their customer knowledge acquisition process, like data quality or data heterogeneity problems. This paper focuses one relationship marketing program that was conceived to be supported by a huge marketing database. Although database's dimension it has many structural problems that had conditioned the initial approach. During his work it was proposed and developed a knowledge discovery in databases process using data mining algorithms in order to answer to marketers' questions: which customers uses a promotional voucher? Which are they main characteristics?. The results show great promise as the predictive accuracy of the integrated ...