The Collaborative Glaucoma Study was designed to test the hypothesis that tests of ocular pressure and its fluid dynamics before and after water drinking can predict those eyes at risk of developing field defects in the future and to describe quantitatively the predictive value of these measures. Ninety-eight of 5886 eyes (1.7%) with elevated pressures developed field damage over 1-13 years of followup. Comparing the eyes that incurred damage with those that did not, five factors were identified as having a standardized coefficient which was statistically significant; these were C-value of tonography, age, applanation pressure, cup/disc ratio and pressure change after water drinking. However, the predictive ability of all five factors--alone or considered cumulatively--was limited. A major contribution of the Collaborative Study may be in highlighting the need to continue the search for factors--perhaps hitherto unsuspected--that influence the development of glaucomatous visual field defects.