The World Wide Web makes knowledge bases freely available and accessible to people worldwide, whether to access a specific resource ("searching via the Web") or to broadly search ("searching the Web") using a variety of search engines, such as AltaVista, Excite, Google, HotBot, Infoseek, Lycos, Netscape, Webcrawler, Yahoo!, and others. Searching involves using a Web-based form to submit a query to a database, most of which might also be accessible via telnet, gopher, or other older, less graphical, and less powerful methods. Clinical searches are commonly accomplished using the freely available National Library of Medicine databases such as MEDLINE and AIDSLINE, which store bibliographic information, including abstracts (in recent years), of articles published in indexed medical journals since 1966; the Web can also access the entire worldwide "electronically published" realm. Search engines, which allow Boolean searches, provide comprehensive lists of all electronic sites containing those keywords and can yield otherwise difficult-to-find information. However, they can also result in a profusion of Web pages with marginal relevance or of extremely low quality; patients and physicians must not assume that information published electronically is as valid as information in textbooks or peer-reviewed journals.