The incidence of valves in the major veins of the lower extremities of Africans and Caucasians was studied. Valves are absent in the inferior vena cava in both races. In the common iliac veins, 1-7% of Caucasians and 1% of Africans have rudimentary valves. Normal valves exist in the following veins: the external iliac veins--22-33% of Caucasians and 9% of Africans; the femoral vein segment above the saphenofemoral junction--67-81% of Caucasians and 93% of Africans; the 3-cm-length of the femoral vein below the profundofemoral junction--90% of Caucasians and 100% of Africans; the terminal 3 cm of the great saphenous vein--100% Caucasians and 98% Africans. The lower incidence in the number of valves in Caucasians may account for the high prevalence (10-18%) of varicose veins in Caucasians; the reverse of this relationship is suggested for the low prevalence (1-2%) of the condition in Africans. Factors influencing the development of incompetent valves are discussed.