Sixty-five Kikuyu infants were developmentally evaluated (Bayley Test) at two-month intervals during the first year of life. Precocity was demonstrated for mental as well as motor test performance. Familial economic status was positively related to infant performance. Social and demographic variables contributed at least 25% to test score variance, and therefore even in the first year, must be considered in evaluation of psychological development of sub-Saharan African infants. (Author)