Medetomidine, a highly specific alpha-2 adrenergic agonist, has been demonstrated to lower intraocular pressure (IOP) in rabbits and cats when applied topically. The purpose of this study was to assess the influence of intravenously injected medetomidine on the pupil size (PS) and the IOP of non glaucomatous dogs. IOP was measured by applanation tonometry and PS was measured using Jameson calipers at t=0 (or time of IV injection of medetomidine (Domitor; Orion) at the dose of 1500 microg/m2 body surface area) and again after 5 minutes (t=5). The IV administration of medetomidine caused miosis in all 14 dogs. The mean PS decreased from 9.0 to 4.0 mm (p<0.001). The IOP was lowered in 10 dogs and in 4 dogs there was a rise in IOP. The mean IOP (mmHg) decreased from 22 to 21 (p>0.2). The data presented above confirm that medetomidine at a dose of 1500 microg/m2 body surface area produces miosis in non glaucomatous dogs, without influencing the IOP.