Two different configurations of a silastic based passive pressure regulating shunt valve for glaucoma filtration surgery are currently being evaluated for incorporation into Molteno type implants. Configuration # 1 utilizes a Molteno implant fitted with a silastic O-ring at its periphery. Configuration # 2 utilizes a Molteno implant fitted with a silastic disk within the central dome of the device. Pressure threshold data were obtained via mechanical transducers and visual techniques, respectively. Comparison was made with respect to threshold pressure, repeatability of data and frequency of leakage after assembly. Preliminary results have shown configuration # 1 to be capable of obtaining threshold pressures of 15 mm of Hg. Threshold pressure was found to be nearly independent of durometer value and directly proportional to the distance between inlet and outlet orifices.