We hypothesize that endothelin-A receptor stimulation contributes to the elevated blood pressure and superoxide production in endothelin-B receptor-deficient rats on a high salt diet. Experiments were conducted on homozygous endothelin-Bdeficient (sl/sl) and wild-type rats (wt) fed a high salt diet (8% NaCl) for 3 weeks. Separate groups were given normal drinking water or water containing the endothelin-A receptor antagonist, ABT-627 (5 mg/kg per day; n = 8-9 in all groups). On a normal salt diet, (sl/sl) rats had a significantly elevated systolic blood pressure compared with wt (138 ± 3 vs 117 ± 4 mmHg, respectively; P < 0.05). High salt diet caused a significant increase in systolic blood pressure in (sl/sl) rats compared with wt (158 ± 2 vs 138 ± 3 mmHg, respectively; P < 0.05). Endothelin-A receptor blockade decreased systolic blood pressure in (sl/sl) rats on high salt (125 ± 5 mmHg; P < 0.05 vs without antagonist) without affecting the systolic blood pressure in wt (119 ± 4 mmHg). Aortic superoxide production (lucigenin chemiluminescence) and plasma 8-isoprostane were elevated in sl/sl rats and were significantly reduced by endothelin-A receptor blockade in sl/sl, but not in wt rats. These findings suggest that endothelin-1, through the endothelin-A receptor, contributes to salt-induced hypertension and vascular superoxide production in endothelin-B-deficient rats.