Abnormalities have been reported in the ECG's of Negroes, American and African, in comparison with Caucasians. Items believed to be more prevalent in Negroes are: T-wave inversion, T-wave inversion with S-T depression, S-T elevation with or without tall T waves, and high R + S amplitude. The responsibility borne by the ethnic factor, malnutrition, or other environmental factors is controversial, as is even the validity of the differences. In an attempt to elucidate the situation, ECG studies have been carried out on young South African Bantu and Caucasians of both sexes, 7–9, 16–19 and 20–29 years of age. The Bantu studied included groups differing in region of dwelling (town and country), nutritional state, infections, habitual activity, and cultural level. Caucasian subjects were drawn mainly from middle class contexts. Some serial studies were undertaken. The main findings are as follows. 1. 1. In agreement with other workers' observations, wide ranges of prevalences of ECG items were found in the Bantu and Caucasian groups examined. 2. 2. Marked changes, particularly in Bantu, were noted occasionally in serial studies; these varied from item to item. However, neither the wide ranges mentioned, nor the serial study changes, are sufficient to preclude comparisons of findings in respect to race, sex, and age. 3. 3. The most conspicuous differences found between Bantu and Caucasians were the much higher prevalences in the Bantu of inverted T waves with S-T depression (Grusin Pattern I) in the young, diphasic T waves, also in the young, and high voltage at all ages studied, as reflected by maximum R + S amplitude. None of these differences between Bantu and Caucasians, or even between the various groups of Bantu of the same sex and age examined, are explicable on the basis of differences in anthropometry, ponderal index, nutritional state, infections, activity, or cultural level. While it is tempting to attribute these ECG differences between Bantu and Caucasians (particularly high voltage) to an ethnic factor, evidence is inadequate to reach a firm conclusion. 4. 4. Regarding sex, a sex difference, slight or conspicuous, was apparent at 7 to 9 years in both races for all ECG items studied. In some items, e.g., T-wave inversion with S-T depression in the Bantu, the differential decreased with age. In others, e.g., tall T waves with or without S-T elevation, also with high voltage, the differences became more pronounced. 5. 5. In respect to age, in some items in both races, e.g., T-wave inversion, diphasic T waves, and high voltage, prevalences decreased with age. In others, e.g., tall T waves in male subjects, prevalences rose. 6. 6. There appears to be no evidence that ECG differences in Bantu have prognostic significance. 7. 7. While Bantu and U. S. Negroes differ from Caucasians in certain ECG items, such differences are not peculiar to Negroes of African origin; like differences are seen in other non-Caucasian populations.