The problem of tuberculosis amongst mental hospital patients is of importance from both the psychiatric and public health point of view. Most of the active methods of psychiatric treatment must be abandoned or discontinued when physical illness intervenes. The problem is even more far-reaching from the standpoint of public health. Wingfield, Trail, Banks and McDougall (1942) have estimated that there is probably a reservoir of 250,000 infectious cases recognized and unrecognized in England, Scotland and Wales, and several authors have pointed out that mental hospitals contribute a disproportionate number to this reservoir. Modern methods of mental hospital administration with parole and leave privileges applied to the maximum number of patients lend importance to the public health aspect, not only the patients themselves and hospital staff being menaced, but also patients' visitors and relatives and other contacts outside hospital. The incidence of tuberculosis in mental hospitals has been variously estimated at 5 to 10 times and the mortality in peace-time 8 or 9 times that of the general population. These figures are sufficient to justify all efforts to bring the problem under control.