1. The Chaga population living on Mount Kilimanjaro are living under conditions which gives them no opportunity of gaining a tolerance for the malaria parasite. 2. At altitudes over 3,500 ft. on Kilimanjaro there is extremely little malaria; below this level there is much malaria and at 2,500 ft. there is a spleen and parasite rate of about 70%. 3. F. falciparum is the predominant parasite met with but P. vivax, P. malariae and P. ovale X are all present in this District. 4. Comparative methods of spleen measurement shew a decrease in the size of the spleen after the age period 0 - 2 years. 5. Four cases of Blackwater "Fever in Chaga natives and three in other tribes from high altitudes have been described. These cases shew a mortality of 25 %. Eight cases of Cerebral Malaria, seven in -zaga and one in a native of Mbulu have also been described; three of these cases died, the others recovered only as the result of energetic treatment. 6. It has been shewn that the adult Chaga is as prone to the pernicious type of malaria, including Blackwater Fever as is the unsalted European. This is not confined to Chaga and cases from other tribes, who have spent their childhood in malaria free areas, have been quoted. 7. Natives from endemic areas can be made liable to the more serious effects of malaria in later life if the acquisition of their tolerance is interfered with by prophylactic measures. (Blackwater Fever case No .5). 8. Expansion of the Chaga, if they are to seek new land at lower levels, is fraught with serious danger from a medical point of view. I t is inadvisable from the employer's and employee's point of view that natives, from the highlands of Kilimanjaro, should work in malarious areas unless adequate prophylaxis and treatment for malaria is easily available.