Recent ethnobotanical investigations have greatly advanced the scientific understanding of the identification, distribution and constituents of plant hallucinogens in the northwest Amazon. To date at least nineteen species employed as stimulants or narcotics have been reported from this region - a figure that represents approximately one-seventh of all known psychotomimetic plants (Schultes and Hofmann 1980). Although this remarkable concentration in part reflects floristic peculiarities, it is also a result of cultural characteristics of the indigenous tribes. Throughout the northwest Amazon, hallucinogenic plants are a very vital feature of religious, medical and magical aspects of life. In the spring of 1981 , whilst we were engaged in ethnobotanical studies in eastern Ecuador, our attention was drawn to a most peculiar use of hallucinogens by the Waorani, a small isolated group of some 600 Indians (cf. Davis and Yost, in press). Amongst most Amazonian tribes, hallucinogenic intoxication is considered to be a collective journey into the subconscious and, as such, is a quintessential social event (Harner 1973, Reichel Dolmatoff 1971, 1975). The Waorani, however, consider the use of hallucinogens to be an aggressive anti-social act; so the shaman, or ido, who desires to project a curse takes the drug alone or accompanied only by his wife at night in the secrecy of the forest or in an isolated house. Under the influence of mii ( Banisteriopsis murieata (Cav.) Cuatr.) the ido can call on the wenae, or malevolent spirits, to wreak evil, but there are no spirits whom he can contact to do good or to counter another ido 's curse. This belief is an unusual exception to the Amazonian pattern in that only the ido who caused the calamity can cure it, which he does by drinking mii to communicate with his wenae to convince them to withdraw from the victim. It places the shaman in a precarious position, in that any agreement by the shaman to cure is a de facto admission of guilt; to agree to cure could easily end in death, so the accusation of being an ido is one that is usually met with defiant denial. Given this belief system, it is easy to see why the ido would inevitably choose to act clandestinely. Of particular botanical interest is the fact that this peculiar cultural practise involves hallucinogenic plants, one rarely used and one until now unreported. The Waorani have two hallucinogens: Banisteriopsis muricata and an as yet undescribed basidiolichen of the genus Dictyonema. The former is morphologically very similar to other commonly used psychoactive malpighiaceous species such as ayahuasca, Banisteriopsis Caapi (Spr. ex. Griseb.) Morton. On the other hand, no basidiolichen has yet been reported to be employed as a hallucinogen.