SummaryNebivolol is a mixture of equal amounts of 2 enantiomers: SR3-nebivolol (d-nebivolol) and RS3-nebivolol (I-nebivolol). SR3-nebivolol is a potent and selective PI-adrenergic antagonist both in vitro and in vivo. Nebivolol acutely lowers blood pressure in spontaneously hypertensive rats and induces a slight decrease in total peripheral vascular resistance and a slight increase in cardiac output in anaesthetised dogs. These haemodynamic effects cannot be explained by PI-adrenergic antagonism and are largely attributable to RS3-nebivolol.