During the last eight years the E.E.G.'s of over 100 persons awaiting trial on charges of murder have been examined, at first at Sutton and since 1947 at the Maudsley Hospital. While a few cases were seen during the war, the majority of these prisoners have been examined since the end of hostilities and about 50 of them between 1948-1950. It is difficult to assess to what extent this group constitutes a cross-section of the murderer population. During the four years 1945-48 inclusive some 300 prisoners were committed for trial at Assizes over the whole country on the charge of murder and this is the stage at which the majority of our subjects have been examined. Some 50 prisoners were examined during this period so that approximately one-sixth of all cases have been seen here. There were no formal criteria of selection, which was usually made by the prison medical officers, but inevitably there has been a greater concentration within the group of individuals suspected of epilepsy or brain disease. Nevertheless, in the last two years the majority of prisoners accused of murder in the London area and home counties have been examined. At the time when the examinations were made, we were supplied in each case with full clinical details and some information regarding the alleged crime by the prison medical officer. By far the largest number of such prisoners has come to us from Brixton Prison. We are greatly indebted to Dr. J. C. Matheson, Dr. Hugh Grierson, Dr. F. H. Taylor, as well as to medical officers of other prisons throughout the country, who have given us all the information available and have collaborated with us in an invaluable way in our investigations.