We administered the endothelin-A receptor antagonist BQ-123 to spontaneously hypertension rats (SHR) and measured choroidal blood flow (CBF) by the hydrogen clearance method (BQ-123 group, n=8). As a control, we adnimistered saline to SHR (control group, n=8). The BQ-123 group demonstrated a significant increase in CBF throughout the period from 15 minutes until 120 minutes after injection. In contrast, the control group did not demonstrate any increase in CBF. These results suggest that endogenous ET-1 may be involved in the decrease in choroidal circulation of SHR and the administration of BQ-123 may inprove it. Since this change was not detected in Wistar rats, it is considered that FT-1 works more strongly in SHR. It is also presumed that the function of ET-1 varies greatly depending on the internal organs and vasculture.