Psychoactive plants have been used by humans for tens of thousands of years during which time their usehas been intimately associated with religion and ritual. Their molecular structures are related to the structure of naturally occurring neurotransmitters in the brain; their effects are primarily on consciousness. Hence research ranging from the chemistry laboratory to field work in shamanic cultures to self-experimentation have all contributed to understanding the relationships between psychoactive substances and transpersonal states. In reviewing the research in this area one often encounters statements such as: "Since the beginning of the 1970s,there has been little new research into psychedelic substances" (Ratsch, 1990,p. 6; also Nichols, 1987).Certainly research ofthe nature and caliber of the classic studies by Leary and Metzner (19671968)on prisoner rehabilitation, Pahnke and Richards (1966) on the induction of mystical experience, and Masters and Houston (1966)on subjective aspects of psychedelic drugs are not currently possible. However, despite the virtual ban on their use in research with human subjects in the U.S. and elsewhere, there has been a major resurgence of research activity in the past ten years. New discoveries in neurochemistry, anthropology and transpersonal psychology have led to significant new findings in many areas, but especially in ethnopsychopharmacology and archeopsychopharmacology. The use of psychoactive substances to assist psychotherapy has continued in Europe. The latter research has been disseminated primarily at conferences and not in the major journals; hence it is unknown to most persons outside this network. Therefore, this reviewwill consider research generated from these sources as well as other areas where research has continued, with a focus on the methods employed.