Open access to the medical literature: How much content is available in published journals?

To understand how much of the published medical journal literature is currently openly available from publishers, we studied 174 journal titles in research and clinical medicine from Thomson Scientific's ISI Citation Databases. Nearly one third of the journals studied have some or all of their recent content freely available through the journal's web site. Forty-six journals (26%) offered their most recent content immediately available without charge; an additional 12 journals (7%) make all content available within a specified period after initial publication. We also considered content back to 1992, a file depth approximately twice the cited half-life of the journals in aggregate. Although 93% of the journals have their current issue and one or more back years available electronically, we estimated that less than 60% of article content since 1992 is electronically available and 21% is open access (OA). Considering other paths to OA (partial open access or e-print archives) would increase this percentage.