At the beginning of the war part of the Maudsley Hospital moved to Mill Hill School, and a neurosis centre of 550 beds was established. During the six years of war some 20,000 neurotic patients, both forces and civilian, were treated at this centre. Within the centre a special unit for the study of Forces patients with effort syndrome (E.S.) was set up. This unit was in existence from 1939 to 1945, and during this period 2,324 cases of E.S. were treated. The writer was associated with this unit throughout, working in association with a cardiologist (Paul Wood (1)), and with other psychiatrists (Lewis (2), Guttmann (3), Gillespie (4)). Much of the material brought together in this thesis has already been published (Jones (3, 5, 6, 7, 8, 9, 10, 11, 12, 38, 43)). During most of the war years the writer was in receipt of a Medical Research Council grant.