In this work we examined the role of adrenergic receptors in the smooth muscles of retinal arterioles, in the control of blood flow. Segments of retinal arterioles from bovine eyes were dissected out and placed in a small vessel myograph. The vessels were continuously bathed in a physiological saline solution with a temperature of 37C and constant oxygen flow. Drugs were added to the bath accordingly (with min. n = 5) and the contractile or dilative response, recorded with the myograph (mN). The effect of the alpha (a) and beta (b) agonist noradrenaline (NA) was tested and evoked a significant contractile response. b-agonists elicited no significant response (unspecific agonist; isoproterenol and b2 specific agonist; terbutalin). An unspecific a agonist (dihydroergotamine) and a specific a1 agonist (cirazoline) elicited significant contractile responses. But a specific a2 agonist (clonidine) did not. Unspecific b blockers (propranolol and timolol) significantly relaxed the contraction induced by NA, but only at high doses. An unspecific a blocker (phentolamine) significantly relaxed the contraction induced by NA and by cirazoline. These results indicate that in the smooth muscles in bovine retinal arterioles,a1 receptors are dominant. NA and cirazoline are mediating their contractile effects through a1 receptors whereas the a blocker phentolamine is blocking this response. It is also likely that b receptors are not present and that the relaxation mediated by the b blockers might be working through other mechanisms than the blockage of b receptors, since they influenced the NA response only at high doses.