Adrenoceptor agonists were used to characterize the α₁-adrenoceptor subtype responsible for mediating tension (phasic and tonic combined) in the denuded rat aorta and compared with radioligand binding at α₁-adrenoceptor subtypes. The rank order of potency at the rat aorta was the same as that obtained for binding affinity at the rat clonal α_1d-adrenoceptor: norepinephrine > epinephrine > cirazoline > phenylephrine > oxymetazoline > A-61603 > methoxamine. Correlation coefficients comparing rat aortic contraction (pD₂) to binding (pK_i were 0.09–0.21 for α_1A/a receptors, 0.66 for clonal α_1b clonal α_1b and 0.94 for clonal α_1d-adrenoceptors. Correlation coefficients comparing the clonal α_1d-adrenoceptor binding affinity to in vitro contractile responses were 0.03 and 0.10 for the rat vas deferens and canine prostate α_1A-adrenoceptor responses, respectively, 0.09 for the rat spleen α_1B and as noted, 0.94 for the rat aorta. The agreement observed between agonist potency at the rat aorta and affinity for the α_1d binding site provide new evidence that the α_1D-adrenoceptor subtype is responsible for mediating contractions in the rat aorta.