Microzonuloscopy, a biomicroscopic technique in which the patient is examined with his head tilted downward 60 degrees, makes possible excellent visualization of the anterior hyaloid membrane. Frequently, when the patient changes fixation from far to near and near to far, the membrane is seen to vibrate. Study of this phenomenon disclosed other characteristics of the membrane. The findings suggest that the membrane plays a role in accommodation and that it may influence aqueous dynamics. © 1969.