The present study was conducted to evaluate effect of sub-acute i.v. injection of ETB receptor agonist IRL-1620 in mice.Swiss albino mice (n = 24, weighing 20-25 g) were divided into two groups (12 animal each), control group (0 μg kg-1) and IRL-1620 treated group (1 μg/kg/min, i.v., for 30 days).Each group was further subdivided into two groups depending on sex of mice having 6 animals each.No significant change in animal body weight, hemogram, liver function test and renal function tests was observed on treatment with IRL-1620.Histol. examination of liver was normal and Kidneys showed mild congestion.In conclusion, sub-acute dose (1 μg/kg/min, i.v.) of endothelin receptor agonist ETB IRL-1620 did not cause toxic effect on liver and kidney.