Objective: The illicit use of hallucinogens is reemerging in the United States, especially among well-educated adults and teenagers. These same groups are also frequent users of the Internet. The authors sought to characterize the extent of information about hallucinogens available to Internet users. Method: Using standard Internet search techniques, the authors located 81 hallucinogen-related sites and categorized the information provided. Results: Internet sites offer thousands of pages of information-albeit of questionable accuracy - on how to obtain, synthesize, extract, identify, and ingest hallucinogens. Much of this information has yet to appear in textbooks. By contrast, the authors found few U.S. government agency sites offering cautionary material about hallucinogen use. Conclusions: Using the Internet, potential hallucinogen users can bypass traditional channels of medical information and learn in great detail how to obtain and use numerous drugs with unknown hazards.