Clinical trial registries could make an important contribution to research by playing a role in the avoidance of trial duplication as well as serving as a source of information on the existence of clinical trials for those wishing to perform overviews. In order to fulfil their role efficiently, these registries should contain information about all trials. However, resources of existing registries are not exhaustive. Currently, all protocols for clinical trials must be submitted to an ethics review board for approval-thus these boards could provide an invaluable source of information about what trials are being performed. One of the objectives of our project was to assess the attitudes of the ethics review boards (ERBs) to providing this type of information to clinical trial registries. We received 115 replies from 281 questionnaires sent to ERBs in seven European countries. More than 70% replied that they would be willing to communicate information about the trials they review, and there seemed to be general agreement that clinical trial registries should be funded and supported by governments. Although ERBs could provide a useful source of information, only an official body such as the Ministry of Health or a drug regulatory body could establish and run a clinical trials registry efficiently.