This paper considers the possible reasons for the relative failure of behavioural treatment for 'ruminations' (obsessional thoughts without overt compulsive behaviour). It is argued that this problem is due to an inadequate conceptualisation of the nature of ruminations and that as a result, exposure and response prevention have not been applied effectively. Effective treatment of ruminations requires systematically applied exposure in conjunction with the identification and prevention of covert compulsive behaviours. The practical problems of implementing 'covert exposure and response prevention' are considered and a form of habituation training is described, which is designed to overcome these inadequacies. A series of single case studies using this technique is presented.