Filtration surgery was performed with a pressure-sensitive, unidirectional valve implant in 79 eyes with neovascular glaucoma. The device consisted of an open Supramid tube (outside diameter 0.58 mm) sealed to a Silastic tube with a slit valve. The Supramid tube was inserted at the corneoscleral limbus 1 to 4 mm into the anterior chamber. The Silastic portion was located under a scleral flap. Of the 79 eyes, 53 had postoperative intraocular pressures less than or equal to 24 mm Hg after a mean follow-up period of 23.7 +/- 10.9 months. Bleb revision for external scarring was required in ten of these 53 eyes and postoperative medical therapy was required in 26. The valve implant failed to control intraocular pressure in 26 of the 79 eyes. Failure was secondary to scarring of the external bleb in 18 eyes and to closure of the internal Supramid tube in five eyes. Mortality during the follow-up period was high: 12 of the 53 successfully treated patients and five of the unsuccessfully treated patients died.