A new instrument to measure episcleral venous pressure was described. The episcleral venous pressure of human eyes was measured by determining the pressure necessary to arrest blood flow with a modified force-displacement transducer. The mean episcleral venous pressure of 39 normal eyes was 9.0 ±1.4 mm Hg (standard deviation) and of 27 eyes with primary open-angle glaucoma was 8.6 ± 1.4 mm Hg. There was no significant difference between these values. The results were compared to those in the literature.