Many people vaguely remember that lysergic acid diethylamide (LSD) and other psychedelic drugs wer eonce used experimentally in psychiatry, but few realize how much they were used, and how long. This was not a quickly rejected and forgotten fad. Between 1950 and the mid-60s more than a thousand clinical papers were published, discussing 40,000 patients. Several dozen books appeared, and six international conferences were held on psychedelic drug therapy. LSD aroused the interest of many psychiatrist who were in no sense cultural rebels or especially radical in thier attitudes. It was recommended for a wide variety of problems, including alcoholism, obsessional neruosis, and childhood autism. Almost all publication and most therapeutic practice in this field have come to an end, as much becasue of legal and financial obstacles as because of any loss of interest. Perhaps those two decades of research and clinical practice, which took up a considerable part of the careers of many respected psychiatrists, should be written off as a mistake, a mistake which now has only historical interest. But it would be wiser to see first whether something can be salvaged from those years, and to see what the story suggests about the boundaries of psychiatry and the meaning of drug use in the field.