Background: Scientific research entails systematic investigation. Publishing the findings of research in peer reviewed journals implies a high level of confidence by the authors in the veracity of their interpretation. Therefore it stands to reason that researchers should be prepared to share their raw data with other researchers, so that others may enjoy the same level of confidence in the findings. Method: In a prospective study, 29 corresponding authors of original research articles in a medical journal (the British Medical Journal) (...) were contacted to ascertain their preparedness to share the data from their research. The email contact was in one of two forms, a general request and a specific request. The type of request a researcher received was randomly allocated. Findings: Researchers receiving specific requests for data were less likely, and slower, to respond than researchers receiving general requests. Only one researcher released data. Most researchers were reluctant to release their data. Some required further information, clarification, or authorship. Interpretation: The general reluctance of researchers to consider requests for their data is of concern. It raises questions about the level of confidence that should be placed on their interpretations of the data. It also highlights an unfortunate situation where researchers are more concerned with losing an advantage than advancing science. (shrink)