Tonographic studies of eyes with aphakic glaucoma have shown impairment of aqueous outflow. There has been, however, little knowledge as to what outflow facility prevailed in such eyes before the lens was extracted and as to the effect of cataract extraction on outflow facility in eyes not developing clinically recognized aphakic glaucoma. The purpose of this paper is to present a comparison of tonographic and gonioscopic studies made prior to and at intervals following cataract extraction in a series of 142 eyes (in 124 patients, 18 of whom had both lenses removed). Method The diagnosis of cataract was made in the Eye Clinic at the Massachusetts Eye and Ear Infirmary. No topical medication had ben instilled during the 48 hours before preoperative tonography. All tonographic and gonioscopic studies were done by one of us (P. F. L.). Tonography, practiced according to the method of Grant, was done at (approximately) 3,