PubMed - A service of the U.S. National Library of Medicine and the National Institutes of Health
MEDLINE - Compiled by the U.S. National Library of Medicine (NLM) and published on the Web by Community of Science, MEDLINE® is the world's most comprehensive source of life sciences and biomedical bibliographic information. It contains nearly eleven million records from over 7,300 different publications from 1965 to November 16, 2005.
The Cochrane Library - The Cochrane Library is a collection of databases that contain high-quality, independent evidence to inform healthcare decision-making.