A suction cup has been devised to fit the periphery of the cornea and applanate its central part. A slow, continuous saline infusion entering through a central opening forms a disc of fluid between applanating and applanated surface in which the pressure (Pcup) is followed by a conventional transducer. The saline leaves the periphery of the cup via a hanging tube creating a suction pressure of approximately 15 mmHg, which keeps the cup on the cornea. In human cadaver eyes the relation between intraocular pressure (Po) and Pcup was Po = 0.80 X Pcup - 2.3 (mmHg), r = 0.9986. In enucleated rabbit eyes: Po = 0.94 X Pcup - 0.1 (mmHg), r = 0.9996. Thus, with appropriate calibration of the recorder, the cup functions both accurately and linearly. The relationships were virtually uninfluenced by large changes in both the rate of suction and the inflow rate of saline. When measuring on eyes of patients, the cup was atraumatic and gave an excellent dynamic response.