A "spontaneous" rise in intraocular pressure during manometry of the anterior segment of the rabbit eye introduces an undesirable variable into an otherwise accurate measurement. The origin of the reaction and the mechanism by which it alters intraocular pressure are not known. The purpose of this paper is first to report an improved method of manometry which avoids the reaction and permits physiologic study for relatively long periods of time in a nonirritated eye, and, second, to discuss the site of origin of the response. A subsequent report will deal with the mechanisms by which the rise in pressure is produced and sustained. The gross characteristics of the "spontaneous" pressure response during manometry resemble those changes induced following trigeminal stimulation either antidromically,1 or by chemical,2,3,4 or mechanical5,6 irritation of cornea, conjunctiva, iris, and lens, or by paracentesis,7 and consist of