Both endothelin-1 and oxidative stress have important roles in the development of cardiovascular diseases such as hypertension and atherosclerosis. Limited information is available on the interaction between oxidative stress, the glutathione system and endothelin-1 in humans. We aimed to investigate the association of endothelin-1 with markers of oxidative stress and the antioxidant capacity in a biethnic South African cohort. This cross-sectional study included 195 black and 198 white South Africans. Serum endothelin-1 levels and oxidative stress-related markers such as reactive oxygen species (measured as serum peroxides), glutathione peroxidase, glutathione reductase, superoxide dismutase and catalase were measured. In single, partial and multiple regression analyses endothelin-1 correlated positively with glutathione reductase activity (adj. R2=0.10; β=0.232; P=0.020) and negatively with antihypertension medication (P=0.02) and tended to correlate with glutathione reductase-to-glutathione peroxidase ratio (adj. R2=0.10; β=0.19; P=0.057) in black men. In white men, endothelin-1 correlated positively with ROS (adj. R2=0.09; β=0.26; P=0.01) and negatively with glutathione peroxidase activity (adj. R2=0.05; β=-0.23; P=0.02). In black women, endothelin-1 correlated negatively with total glutathione (adj. R2=0.22; β=-0.214; P=0.026). Endothelin-1 may contribute to glutathione reductase upregulation through increased reactive oxygen species production mediated via endothelin-1 in black men. In white men, we observed a negative association between glutathione peroxidase and endothelin-1, describing the expected physiological relationship between endothelin-1 and reactive oxygen species. Higher total glutathione levels may act as a counter-regulatory mechanism to protect against oxidative vascular damage attributed by endothelin-1 in black women.