Changes of anterior chamber volume with its consequent changes of intraocular pressure (IOP) were found to alter the rate of aqueous humor formation. It appears important that the eye pressure changes exert their influence when they are brought about by variations in aqueous humor volume. In a previous communication, the elevation of the IOP by occlusion of the anterior ciliary vein had no inhibitory effect on aqueous humor formation. The technique described here can be used for the elucidation of drug effects, but only under the condition that the amount of fluid removed from the anterior chamber exactly equals that being perfused through the posterior chamber. In this way no eye pressure change is introduced which could either increase or decrease the aqueous humor inflow rate.