Prolactin release from primary cultured pituitary cells was investigated using a dynamic perifusion system. Although epinephrine (1 µmol/l) produced an elevation in the mean value of the prolactin concentration at the onset of the perifusion, the elevation was not statistically significant, and the overall effect of the epinephrine was to produce an inhibition of prolactin release. The α-and D2-receptors of the primary cultured cells were functionally removed by a pretreatment with phenoxybenzamine (0.1 or 1 µmol/l). Since phenoxybenzamine irreversibly inactivates both the adrenergic α- and the D2-receptors but does not block the β-receptors, the enhanced stimulatory action of the epinephrine (1 µmol/l) on the phenoxybenzamine pretreated cells suggests the involvement of adrenergic β-receptors in prolactin release. Perifusion of isoproterenol (1 µmol/l), a β-receptor agonist, stimulated prolactin release. This stimulation was blocked by β-receptor antagonism with propranolol (1 µmol/ 1) supporting the implication of the β-receptor in prolactin release. In order to differentiate between βι- and β2-receptor involvement, we investigated the effects of ICI 118,551 (1 µmol/l) on isoproterenol-induced prolactin release. ICI 118,551, a selective β2-receptor antagonist, blocked the stimulatory action of isoproterenol on prolactin release indicating that the β-receptor responsible for the stimulation of prolactin release belongs to the β2-receptor family. Moreover, the demonstration that salbutamol, a selective β2-receptor agonist, stimulated prolactin secretion offers further evidence in support of the role of the β2-receptor in the stimulation of prolactin release. In conclusion, our pharmacological studies suggest that primary cultured lactotrophs possess adrenergic β-receptors, and it is the β2-receptor that imparts a stimulatory influence on prolactin secretion.