Examples are given of the use of large research databases for knowledge discovery. Such databases are not only increasingly used for research in the 'hard' mathematics-based disciplines such as physics and engineering but also in more 'soft' disciplines, such as sociology, psychology and, in general, the humanities. In between the 'hard' and the 'soft' disciplines lie disciplines such as biomedicine and health care, from which we have selected our illustrations. This latter area can be subdivided into: (1) fundamental biomedical research, related to the 'hard' scientific approach; (2) clinical research, using both 'hard' and 'soft' data and (3) population-based research, which can be subdivided into prospective and retrospective research. The examples that we shall offer are representative for using computers in scientific research in general, but in medical and health informatics in particular.