Fifty-four normal tension glaucoma cases were studied to determine the value of several clinical tests for predicting the progression of the disease. Outflow facility, intraocular pressure (IOP) increase after water drinking, and diurnal changes in IOP were studied. Progression was determined on the basis of changes in visual sensitivity as measured on the Octopus 201. A minimum of four examinations of the central 30 degrees were conducted over a 3- to 7-year period. Progression of visual field defects was seen in 38.5% of eyes that had demonstrated some degree of abnormality in at least one of three clinical tests, while only 10.7% of those eyes that appeared normal on the basis of these tests showed such progression. The difference was significant (p < 0.04). These results suggest that the three clinical tests may be of value in detecting normal tension glaucoma eyes at risk for progression of visual field defects.