The rate of aqueous humor production (measured by the clearance of 125I-labeled albumin administered into the anterior chamber) and the intraocular pressure (measured via an electronic transducer) fell after subconjunctival injection of 37 mg (0.3 ml) of etamsylate (Dicynone) in rabbits. The differences between treated and untreated animals with respect to both variables were statistically significant. It is conjectured that the action of etamsylate in lowering intraocular pressure may be mediated at least in part by its reduction of aqueous humor formation.