The National Institutes of Health (NIH) implemented a policy on data sharing in 2003. The policy reaffirmed the principle that data should be made as widely and freely available as possible while safeguarding the privacy of research participants, and protecting confidential and proprietary data. Restricted availability of unique resources upon which further studies are dependent can impede the advancement of research and the delivery of medical care. Therefore, research data supported with NIH funds should be made readily available for research purposes to qualified individuals within the scientific community.  One approach to sharing data is to establish a network of databases. However, there are a number of barriers to creating successful networks, which can include fundamental differences in informatics infrastructure and communication tools used at various research sites. Solutions will entail standards for data collection, processing, and archiving to allow interoperability among the databases and the ability to query data across databases. Open architectures for data collection as well as software to facilitate communication across different databases are needed.