The establishment of the relative validity of tonography on rabbit eyes has permitted an evaluation of the partial suppression of aqueous secretion by acetazoleamide.* In addition to acetazoleamide, three compounds have been observed by tonometry to lower intraocular pressure in rabbits.† These compounds are vasopressin (β-hypophamine; Pitressin), chlorpromazine (Thorazine), and phentolamine methanesulfonate (Regitine). It was the purpose of the present study to determine the effects of these compounds on aqueous flow by means of repeated tonography. Methods Male albino rabbits (Haskins Rabbitry, St. Louis) were used. Tonographic tracings were obtained with use of only topical anesthesia (tetracaine, 0.5%), as previously described.1 By convention, tonography was carried out on the right eye first. In preliminary experiments it was found that the intraocular pressure and facility of outflow in most rabbits were approximately normal 60 to 90 minutes after the initial tonogram. Consequently, a recovery period of at least one hour,