The interaction between several adrenergic agonists (epinephrine, norepinephrine and isoproterenol) and relatively specific beta1- and beta2-antagonists has been examined on fluid permeability of the isolated rabbit ciliary epithelium. A specific beta1-antagonist (metoprolol) had little effect on the permeability increase induced by the agonists, whereas butoxamine (a specific beta2-antagonist) caused an inhibition of the normal agonist-induced permeability increase. The data suggest that these three adrenergic agonists primarily affect the beta2-receptor in the ciliary epithelium in order to induce their effects on fluid permeability.