Analyses of the genetic material in both inherited and acquired diseases such as cancer are already part of the repertoire of many laboratories. Over the last ten to fifteen years research has revealed a very complex human DNA, and shown that the molecular basis for disease is both intricate and variable. Methods for detecting the various categories of genetic changes are needed. These methods should be simple, quick and easy to perform, and cost-effective, and at the same time be both specific and sensitive. No single technology can fulfil all these criteria, and a variety of methods has therefore been introduced. In this overview we describe the different methods and their strengths and limitations.