Background. It is recognized that endothelins are released in response to hypoperfusion and anoxia of the kidney and may be responsible for the consequent deterioration in renal function. This study examined the ability of a non-selective (SB209670) and ETA-selective (UK-350,926) endothelin antagonist to attenuate ischaemia-induced renal failure in unilaterally nephrectomized rats.Methods. The animals were anaesthetized, drug infusion commenced, and the renal artery occluded for 30 min. The endothelin antagonists were given for 30 min before, during, and 60 min after the ischaemic period, at 10, 30 and 100 mug/kg/min or for 60 min after the start of reperfusion.Results. On day 1, following 30 min renal artery occlusion, there was a 95% reduction in glomerular filtration rate, an 8-10-fold increase in plasma creatinine, and 10-15-fold increases in fractional excretions of sodium and potassium, which were partially resolved on day 3 and normalized on day 8. The lowest dose of SB209670 was without effect on the renal functional responses but they were blunted (all P<0.05) by the highest dose. At 30 and 100 mug/kg/min UK-350,926, the decreases in renal function subsequent to the ischaemic challenge were attenuated. Administration of UK-350,926 at 100 mug/kg/min for 1 h starting 60 min after the start of reperfusion, had no effect on the magnitude of the renal disturbances over the first 3 days.Conclusions. The data show that both the ETA/ETB and selective ETA-receptor antagonist ameliorated the ischaemia-reperfusion injury when given in the periischaemic period but not when the ETA-receptor antagonist was given for 60 min at 100 mug/kg/min after the ischaemic period.