1. The effects were examined of two approximately isoenergetic diets differing widely in saturated fat content on the levels of serum cholesterol and triglycerides of nomads and non-nomads in eastern Niger. Each person was also examined for clinical and electrocardiographic evidence of heart disease.2. No significant differences could be found between serum cholesterol and triglyceride levels of 297 Anagamba nomad men consuming 73 % energy as fat and 303 Kanouri sedentary men consuming 9 % energy as fat.3. Rheumatic heart disease was common in nomads and four possible cases of ischaemic heart disease were found in sedentary men only.