1. The effects of minute amounts of dlysergic acid diethylamide tartrate (L. S. D.) on normal subjects, with an age range of 19-48 years, and some psychotic patients of the schizophrenic, depressive, and paranoic type are reported.2. Psychotic phenomena and alterations of the autonomic nervous system were observed. The psychotic phenomena were predominantly schizophrenia-like symptoms that were manifested in disturbances of thought and speech; changes in affect and mood; perception; production of hallucinations and delusions; depersonalization and changes in behavior. The basic intelligence was not reduced.3. Electroencephalographic examinations at the height of the L.S.D. reaction revealed only slight changes, principally increased alpha rhythm, except in one case where there occurred a slowing of about 2 cycles per second.4. Rorschach tests showed abnormalities principally of the schizophrenic or paranoic type. Concrete-abstract thinking tests also, on the whole, showed responses similar to those obtained in schizophrenic patients.5. No scientific theory for the origination of the natural psychotic phenomena or psychoses is being advanced, but the belief is expressed that experimental psychiatry progresses in the right direction.Abstract Teaser