At a conference held at the 12th Session of the German Society for Medicinal Plants Studies, held in Berlin in May 1964, R.E. Schultes took stock of 50 years of ethnobotanic research on American hallucinogens. At least 40 plant species with psychotropic effects were removed, and findings in this area seem far from exhausted. R.E. Schultes has been specially engaged in identifying American hallucinogens since 1936. Many years of the North American Indians and the peoples of Mexico and the Amazon and Andean regions have allowed him to take stock of the situation and to realize how much remains to be cleared in this area. R.E. Schultes has chosen to present the plants studied according to their botanical belongings.