During target validation, researchers attempt to modulate the activity of potential drug targets in relevant cell and/or animal disease models in order to identify those that might be expected to have therapeutic benefit in human patients. This has become increasingly important with the large expansion of potential targets identified by the human genome project and as a result of the spiralling costs of bringing drugs to market. This review will present an overview of the target-validation mechanism and examine the strengths and weaknesses of using oligonucleotide-based technologies such as antisense, short interfering RNA and aptamers.