Inclusion of domain knowledge in a process of knowledge discovery in databases is a complex but very important part of successful knowledge discovery solutions. In real-life data mining development, non-structured domain knowledge involvement in the data preparation phase and in the final interpretation/evaluation phase tends to dominate. This paper presents an experiment of direct domain knowledge integration in the algorithm that will search for interesting patterns in the data. In the context of stock market prediction work, a recent rule induction algorithm, PA3, was adapted to include domain theories directly in the internal rule development. Tests performed over several Portuguese stocks show a significant increase in prediction performance over the same process using the standard version of PA3. We believe that a similar methodology can be applied to other symbolic induction algorithms and in other working domains to improve the efficiency of prediction (or classification) in kn...