This talk will describe the basic research being carried out to determine the changes that occur in the brain when drugs are taken that result in the development of drug dependence. I shall first provide an overview of the field of research, with examples of the type of studies that are being carried out, then the talk will concentrate on the work of my own research group. This is directed firstly at the understanding of the mechanisms ofthe alterations in the central nervous system that are responsible for the frequent relapses during abstinence. Secondly we are studying the effects of stressful experience and aiming to identify the changes that take place in brain function that are caused by stress, that may be involved in the development of dependence. The ways in which research of this type will provide new approaches to the treatment of dependence in the future will be described.