Most clinical practice guidelines were developed by searching only PubMed and the Igaku Chuo Zasshi database of journal articles published in Japan. The Minds, a medical information service supplied by the Ministry of Health, Labour and Welfare of Japan, has published 75 clinical practice guidelines through its web site. Of these guidelines, 76% described search strategies for finding articles as evidence of their development. All guidelines used the PubMed database, and 82.5% used the Igaku Chuo Zasshi database. Only 1.9% to 3.8% of articles were found only in the Cumulative Index to Nursing and Allied Health (CINAHL) database. Forty-nine articles (7.0% of all cited articles) were included in no databases because they were either too old or in a minor journal. Librarians assisting the development of clinical practice guidelines should pay attention to the limits of databases.