NORADRENALINE (NA) is a putative neurotransmitter, possibly involved in mediation of information transfer across synapses in the mammalian central nervous system (CNS)1, whose postsynaptic effect is exerted, in part, by stimulation of β-adrenoceptors coupled to adenylate cyclase 2. Although the rat cerebellum is known to contain NA3, and an afferent noradrenergic pathway has been found4-7, little information is available concerning the noradrenergic synapses there. Indirect evidence such as increase in cyclic AMP content and inhibition of spontaneous electrical activity in rat Purkinje cells8-10 (reduced by β-adrenoceptor blocking8), suggests, however, that such synapses are present and that the postsynaptic NA receptors are of the β type. β-adrenoceptors were identified in homogenates of whole rat cerebellum by a binding assay which used the β-adrenergic antagonist 3H-(-)- alprenolol11. We have now developed a direct in vivo method, using 9-amino-acridin-propranolol (9-AAP), a potent fluorescent β-adrenergic blocker, as a fluorescent probe, in an attempt to detect β-adrenergic receptors in rat cerebellum.