Local pO<sub>2</sub> was measured close to the ciliary process of the rabbit eye using polarographic microelectrodes under microendoscopic observation. The experiments were performed in 5 anaesthetized New Zealand rabbits. Changes in local pO<sub>2</sub>, intraocular pressure (IOP) and blood flow velocity (BFV) were investigated after intra-arterial and topical application of epinephrine. After intra-arterial epinephrine, a simultaneous decrease in BFV, IOP and local pO<sub>2</sub> was found. pO<sub>2</sub> decrease was more pronounced in the anterior part of the ciliary processes than in the posterior part. Topical epinephrine lead to similar changes of all parameters mentioned above, the time constants being 10-20 times longer. In these topical experiments, no recovery of local pO<sub>2</sub> was found over a period of at least 30 min despite an increase in BFV. Our results indicate that in the hyperemic phase after epinephrine the activity of the ciliary epithelium (and probably the total aqueous formation) is higher than normal. Thus, the decrease in IOP in this phase must be due to an increased outflow facility.