A 30-year-old male with manic-depressive psychosis took in 30ml of undiluted Smithion to commit suicide. Ten hours or so later, he was found in state of subconsciousness and admitted into our hospital.1. From the initial trance, he fell into a twilight state. After suffering from an amnestic syndrome and encountering difficulties in concentrating his attention, he was found in a depressive state on the 18th day. This depressive state was presumably a recurrence of the depression with which he had once suffered and therefore proved different from the depressive state unique to organophosphate poisoning.2. In respect to the psychatric symptoms caused by acute and subacute organophosphate poisoning and its sequela, a study is made on the basis of literature to make some comment.3. After a clinical course of two-and-a-half years, it was found that there were a slight degree of disturbance to registration and a drop in mental capacity. These were considered sequelas. These symptoms would not hamper his everyday life, but there were signs of a rise in the sense of quilty conscience and misery when he was in a depressive state.4. EEG indicates that the waves were slowing and paroxismal or sporadic small spikes. Two years later, EEG-findings were slightly abnormal with many sporadic slow α waves. No abnormalities were observed in computerized tomogram.