The vasoconstrictive effect of .alpha.-adrenoceptor agonists was studied on isolated perfused kidney from normal Wistar rats. Methoxamine (ED50 = 1.61 .+-. 0.16 .times. 10-6 M; mean .+-. standard error of the mean), phenylephrine (2.33 .+-. 0.16 .times. 10-6 M) and .alpha.-methylnoradrenaline [.alpha.-methylnorepinephrine] (1.60 .+-. 0.40 .times. 10-6 M) acted as full agonists. Dopamine (9.5 .+-. 1.08 .times. 10-5 M) had a partial agonistic effect. Clonidine and B-HT 920 [alefexole hydrochloride] were inactive up to the concentration of 10-4 M. Prazosin, but not yohimbine (10-6 M) antagonized the response to phenylephrine (pA2 = 8.48 .+-. 0.12) and to .alpha.-methylnoradrenaline (8.02 .+-. 0.10). Apparently, the postsynaptic .alpha.-adrenoceptors which when stimulated increases vascular resistance of isolated rat kidney, belong exclusively to the .alpha.1-subtype.