Forty patients classified as high responders (GG) to dexamethasone testing (intraocular pressure > 31 mm Hg) without visual field loss were subjected to plasma cortisol suppression testing. After a five-year follow-up adequate data were available on 35 patients. Eighteen responded to 1.0 mg of dexamethasonediphenylhydantoin suppression testing in a similar fashion to patients with primary open-angle glaucoma while 17 responded in a similar fashion to subjects classified as low (NN, intraocular pressure<20 mm Hg) and intermediate (NG, intraocular pressure 20 to 31 mm Hg) responders to dexamethasone testing. Eight of the 35 patients developed glaucomatous visual field loss during the follow-up period. These eight patients were not more sensitive to suppression of plasma cortisol than the 27 patients maintaining normal visual fields. Thus, plasma cortisol suppression testing failed to predict the development of primary open-angle glaucoma in GG responders.