'Craving is generally considered a significant factor in opiate addiction that is associated with drug-dependence and in relapse to drug use after treatment'—ARC expert consensus (Pickens and Johanson, Drug and Alcohol Dependence 30: 127-131). There are however difficulties in defining craving and urges to use drugs and in associating craving with drug use and relapse. Tiffany [Psychological Review 97(2): 147-168] has reviewed a considerable number of studies that associated reports of craving with consumption measures of drugs and revealed only an overall modest correlation of 0.4. These findings call into question the general assumption that subjective cravings are invariably associated with drug use. Furthermore, it led to Tiffany's provocative argument that cravings are not necessary for drug use. We have addressed these issues by using a range of complementary techniques derived from research in related fields such as the cognitive psychology of anxiety and depression, physiological response measurements and positron emission tomography (PET) neuro-imaging. Initially we developed computerized assessments to probe cognitive dysfunction in addiction that related to biased processing of automatic thoughts and beliefs about craving and drug use in opiate-dependent subjects and alcoholics. Subsequently in an attempt to develop a reliable method of inducing craving we explored an imagery-based technique that relied on the memory of craving experiences. These experiments were conducted both in opiate addicts who had achieved abstinence and in those undergoing detoxification. Finally, we have begun a study to understand the neural mechanisms of craving using imagery-based procedures at the same time as performing PET studies of regional blood flow using the O15 -labelled water technique.