In light of recent specific liberalizations in drug laws in some countries, I have investigated the potential of entheogens (i.e., psychoactive plants used as spiritual sacraments) as tools to facilitate existential intelligence. "Plant teachers" from the Americas such as ayahuasca, psilocybin mushrooms, and peyote, and the Indo-Aryan soma of Eurasia are examples of entheogens that have been used in both the past and present. These have all been revered as spiritual or cognitive tools to provide a richer cosmological understanding of the world for both individuals and cultures. I used Gardner's (1999a) revised multiple intelligence theory and his postulation of an "existential" intelligence as a theoretical lens through which to account for the cognitive possibilities of entheogens and explore potential ramifications for education. (Contains 6 notes.) [Published September 2004.]