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The physiological and maximum lengths of the femora and tibiae from 288 skeletons of South African Negroes were investigated for evidence of secular changes. The material was arranged in putative 5-year birth cohorts from 1880-1884, 1890-1894 up to 1930-1934 inclusive. The mean values showed a general, but statistically insignificant, decline over the years in question, amounting to 9.0 mm in the femur and 7.0 mm in the tibia. The absence of a secular trend is discussed in relation to the social history of the South African Negro, the positive secular trend found in the San and the negative secular trends shown by most African groups from previous investigations. It is unlikely that the absence of a secular trend denotes the attainment of a genetically determined ceiling to the physical size of these subjects. Indeed it seems more likely that the meliorating factors which are believed to produce a positive secular trend were absent in the years from which our skeletal samples were drawn and signs of improve­ment in these factors are so recent that evidence of their effect is not yet available.