For many years most of us have been aware of the psychoactive effects of Peyote. More recently in drug−oriented literature there have been numerous references to other cacti believed to have hallucinogenic properties. Among these are Doñana from northern Mexico, San Pedro from the Andes, three related mescaline−bearing species from South America, and at least 15 species used by the Indians of Central Mexico as Peyote substitutes. Botanists and Chemists are now studying the constitutes of these cacti and are making some remarkable discoveries. In this guide we will consider each of these cacti and bring the reader up to date on what scientists have learn ed about them. The various methods of using these cacti are also discussed. Directions are given for cultivating cacti and increasing the yield of mescaline and other alkaloids. There are instructions for extracting mescaline from Peyote and San Pedro, and mixed alkaloids from Doñana and other cacti. We also include a brief discussion of the legal aspects of these hallucinogenic cacti and give the names and addresses of legitimate suppliers from whom these plants can be obtained at reasonable prices.