The effects of electrical stimulation of the orbital parasympathetic pathway in the cat on the chamber angle and meshwork and on the intraocular pressure,1,2 as reported previously, pointed towards a possible associated increase in the facility of outflow of aqueous. This possibility was specifically investigated in 105 experiments in the anesthetized cat, as well as in the enucleated eye. The results, which will be the subject of this communication, revealed that during parasympathetic stimulation there was a marked increase in the facility of outflow which was due entirely to the activity of the ciliary muscle rather than to the associated constriction of the pupil. Techniques This presentation will be limited to the details of the constant-pressure perfusion and the constant-rate perfusion techniques, because they provide a measurement of the outflow facility which is independent of the elasticity constant of the eyeball and of elasticity changes that might accompany Parasympathetic