TWO DECADES AGO Hofmann ' accidentally discovered the hallucinogenic activity of d-lysergic acid diethylamide (LSD-25). Its ability to induce a "model psychosis" makes it an excellent laboratory device for the study of psychotic-like phenomena. LSD-25 has also been employed as an adjunct to psychotherapy because recall of repressed memories is enhanced and ego defensiveness to conflict laden material is reduced. Interest in this indole increased when it was found to be a serotonin antagonist that altered cerebral synaptic transmission. Almost 1,000 articles have reported on every aspect of its chemical, biological, and psychological activity. A substance capable of evoking such profound psychic symptoms as delusions, hallucinations, depersonalization, and euphoria or depression could be expected to have serious side effects. For this reason a survey of investigations using LSD-25 was carried out in 1960. The results of this inquiry and of a literature search revealed very few toxic or psychologic complications.