Three types of sleeping sickness are described as occurring in Nigeria— the mild type, the toxic and the nervous. The great majority of the cases found at sleeping sickness surveys belong to the first group. Patients suffer from occasional attacks of headache and fever and from some weakness, very little else. It is their increased susceptibility to intercurrent diseases which often caused the depopulation found in some of the more heavily infected areas. In the second group, which is much more rare, toxaemia is the salient feature. In the third, there are signs of progressive nervous involvement. The proportion of patients suffering from the three types varies. Even in the more virulent epidemics the mild form is common. In Northern Nigeria there is a striking correlation between the areas of infection and the lines of communication, railways, roads, and mining areas. The main zone is confined to the central part of the country. Peripheral areas, though heavily infested with tsetse-fly, are still practically free from infection. Nigerian policy is to establish convenient permanent treatment centres once a full survey of the whole population has been followed by mass treatment. The information obtained at the survey makes the planning of effective protective measures possible. The work of the sleeping sickness teams, dispensaries and the control of mines labour is described. From 1931 to 1943 a total of 3,148,069 people were examined in new areas and 306,322 cases found, an infection rate of 9·7 per cent. In the worst areas 913,718 people were re-examined and an infection rate of 2·2 per cent. found. During the first 5 years of this period the disease was still increasing. The average infection rate was 13·6 per cent. In the next 5 years the spread had been stopped though the infection rate was still high in the remaining new areas. From 1941 onwards the new areas discovered had a low infection rate. The rate for resurveys of what were formerly some of the worst areas was 2·5 per cent. Taking Northern Nigeria as a whole, it is doubtful if there is much more than a tenth of the old amount of infection. The sleeping sickness dispensary system has been expanded during the last few years. Some 80,704 cases of sleeping sickness have been treated. Practically all were voluntary attendances. The general medical and health work also has been improved. With the 43,674 cases treated at general medical stations, a total of 450,451 cases have been treated in the last 13 years. Of these about 400,000 were new cases, the remainder relapses. ' The control of the disease by communal clearing campaigns is described. So far about 240,400 people have been protected from any serious risk of contracting sleeping sickness.A brief account is also given of the Zaria sleeping sickness settlement scheme. So much attention has been paid to all aspects of rural planning and development in the settlement area that it has come to be regarded as a model of rural development. The changes in population figures, particularly in Zaria Emirate, give a striking indication of what has been accomplished. In the period 1923–1933, when the disease was increasing, the population fell by about 12 per cent. At the survey of the whole Emirate 78,000 cases were diagnosed and treated, an infection rate of 20 per cent. There was direct evidence of correlation between infection rates and mortality. With the decrease in sleeping sickness consequent on treatment and control, depopulation stopped. Since 1933 the total population has increased about 24 per cent. It is not claimed that results of treatment have been as valuable in the milder area where there was no sign of the disease causing immediate loss of population. The general position is much more satisfactory throughout the country though constant vigilance is necessary if this relative improvement is to be maintained.