Elevated plasma levels of cytokines such as endothelin-1 (ET-1) have been shown to be associated with sickle cell disease (SCD). However, the role of ET-1 in the pathophysiology of SCD is not entirely clear. We now show that treatment of SAD mice, a transgenic mouse model of SCD, with BQ788 (i.p. 0.33 mg/Kg weight/day for 14 days), an ET-1 receptor B antagonist (ETB), induced a significant decrease in Gardos channel activity (1.7 ± 0.1 to 1.0 ± 0.4 mmol/10¹³ cell x h, n=3, p=0.019) and reducing the erythrocyte density profile by decreasing the D₅₀, (n=4, p=0.012). These effects were not observed in mice treated with BQ123, an ET-1 receptor A antagonist (ETA). A mixture of both antagonists induced a similar change in density profile as with BQ788 alone that was associated with an increase in mean cellular volume and decrease in corpuscular hemoglobin concentration mean. We also observed in vitro effects of ET-1 on human sickle erythrocyte dehydration that was blocked by BQ788 and a mixture of ETB/ETA antagonists but not ETA antagonist alone. These results show that erythrocyte hydration status in vivo is mediated via activation of the ETB receptor leading to Gardos channel modulation in SCD.