PURPOSE: To explore recent studies and clinical experience involving the importance of 24-hour control of intraocular pressure (IOP) in patients with glaucoma. METHODS: Roundtable discussion. RESULTS: During the discussion, the following concepts were identified: 1. Although the effect of IOP is continuous, IOP is infrequently measured in clinical practice. 2. Within an individual patient, measurements of IOP have considerable variability throughout 24 hours. 3. Recent studies have shown that healthy subjects and glaucoma patients may experience their highest IOP at night once they have lain down to sleep. 4. Low blood pressure levels related to an individual's circadian rhythm can occur simultaneous with high IOPs at night, reducing blood flow to the optic nerve head below critical levels and thus resulting in optic nerve damage. 5. Glaucoma medications that can maximally reduce IOP over 24 hours and minimally influence blood pressure should have theoretical and practical advantages for glaucoma management. CONCLUSIONS: The new knowledge about peak night-time IOPs is changing how physicians manage their patients in terms of drug selection and targeted IOP levels aimed at halting progression of glaucomatous optic nerve damage and visual field loss. Physicians are also taking into consideration the troublesome relationship between lowered systemic blood pressure and elevated IOP during the nighttime period. © 2002 by Elsevier Science Inc. All rights reserved.