We clarified whether the intraocular pressure (IOP) response elicited by stimulation of the cervical sympathetic nerve (CSN) is influenced by changes in the baseline of IOP level and by β-adrenergic blockade. The CSN was stimulated electrically for 30 seconds (10 V, 0.1-100 Hz, 2 milliseconds pulse duration) in urethane (100 mg/kg i.v.)-chloralose (50 mg/kg i.v.)-anesthetized, paralyzed cats. The IOP was monitored manometrically, and a controlled saline infusion was delivered into the anterior chamber to gradually increase IOP. CSN stimulation was delivered at the various baseline IOP levels so obtained. When required, a β-adrenergic blocker timolol (2%) was delivered into the conjunctival cul-de-sac. The normal IOP in our cats was 25±3 mmHg. This value decreased transiently on CSN stimulation. The amplitude of this IOP response depended on stimulus frequency and the pre-stimulus baseline IOP level. Topical administration of timolol increased the IOP response to CSN stimulation at a given baseline level. These results suggest that β-adrenergic blockade increases the α-adrenergic mediated-IOP reduction elicited by CSN stimulation at given baseline IOP level.