The anterior chamber of one eye of anesthetized rabbits was surgically opened, simulating the condition which exists prior to cataract extraction in man. Compared to the control eye, the weight of the lens and vitreous was found to diminish at an average rate of 5 mg/min. If it is assumed that the observed weight loss is due to loss of vitreous water, the volume of the vitreous compartment will have diminished by 50μl ten minutes after opening the anterior chamber. This volume is comparable to that lost from the vitreous body as a result of preoperative administration of hyperosmotic agents. It is speculated that the fluid loss from the vitreous body resulting from opening the anterior chamber will not be affected by preoperative maneuvers used to reduce the volume of the vitreous compartment.