Introduction: A common problem in conducting a systematic review is that appropriate data are not available from reports of clinical trials. A reviewer is then faced with the prospect of contacting the primary investigators to request such information. Exactly how one should go about this is not clear. Is it necessary to excite their interest first, or is it safe to ask for data at the outset? How should they be contacted? Is it worth putting great efforts into tracking investigators down? We present the protocol for a multicentre randomised trial of two contrasting, but practical, approaches to contacting primary investigators. We appeal to Cochrane reviewers who face the prospect of contacting six or more independent trialists to collaborate in the study. Such a collaborator will follow a guideline protocol for conducting a mini-trial of specified approaches to requesting information on trial conduct or missing data. Two outcomes will be collected: whether contact is established and whether appropriate information is obtained. Central randomisation will take place at the UK Cochrane Centre. For further information please contact the first author.

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