The adrenocorticotropic hormone of the pituitary (ACTH) is now being used in the treatment of many disorders1such as rheumatoid arthritis, lupus erythematosus, periarteritis nodosa, dermatomyositis, rheumatic fever, allergic states and other conditions involving mesenchymal tissue. The effect of this substance on the course of infections, neoplastic diseases, metabolic disorders, myopathies and mental illness is also being evaluated. The present investigation was undertaken in order to study the nature of electroencephalographic abnormalities and neuropsychiatric disturbances which had been noted incidentally in patients treated initially with this drug. Altogether, 15 patients treated with pituitary adrenocorticotropic hormone were studied at the Columbia-Presbyterian Medical Center. Thirteen of these patients on the medical service2had the following diagnoses: rheumatoid arthritis, 8 cases; dermatomyositis, 2 cases; toxic diffuse goiter, 2 cases, and regional ileitis, 1 case. In addition, 2 patients with schizophrenia were observed at the New York State Psychiatric Institute. The accompanying