Beta-adrenoceptor binding sites were characterized in duck cerebral cortex by an in vitro binding technique, using [3H]dihydroalprenolol ([3H]DHA) as a receptor-specific radioligand. The specific binding of [3H]DHA to duck cerebral cortical membranes was found to be rapid, stable, saturable, reversible, and of high affinity. Saturation analysis resulted in a linear Scatchard plot suggesting binding to a single class of receptor binding sites with high affinity (Kd = 1.18 nM) and high capacity (Bmax = 162 fmol/mg protein). Competition studies showed the following relative rank order of potency of various compounds to inhibit the [3H]DHA binding: antagonists - ICI 118,551 > S(-)-propranolol >> betaxolol, yohimbine, WB-4101, prazosin, mianserine; agonists - isoprenaline @ fenoterol > salbutamol >> clonidine, phenylephrine. The obtained data suggest that in duck cerebral cortex beta-adrenergic receptors (like those described in brains of chick and pigeon) are of the beta2 subtype. This is in contrast to what has been reported for the mammalian brain, where - among b-adrenoceptors - the beta1 subtype is predominant.