PURPOSE: To evaluate the usefulness of day-long sequential office measurements of intraocular pressure (IOP) to make therapeutic decisions in patients with progressive glaucomatous damage despite apparently 'controlled' IOP. METHODS: We reviewed the records of 93 consecutive glaucoma patients (185 eyes) who underwent sequential office IOP measurements (every hour from 7 AM to 5 PM on a single day). These included 53 patients with normal-tension glaucoma (NTG), 12 glaucoma suspects (GS), and 28 patients with primary open-angle glaucoma (POAG) whose visual field deteriorated despite apparently 'controlled' IOP. Only one eye per patient was included in the study. RESULTS: The pattern of the day-long IOP curve was similar in the 3 groups of patients. IOPs were highest in the early morning hours in all groups. The mean +/- SD of the IOP range was 5 +/- 2 mm Hg. An IOP > 21 mm Hg was found in 3 eyes (3%), whereas a range of IOPs > 5 mm Hg was detected in 33 eyes (35%). In the NTG group, there was a significant correlation between visual field deterioration and the peak and range of IOP (P = 0.0002 and P = 0.05, respectively). CONCLUSIONS: Day-long sequential office IOP measurements are useful in selected patients who demonstrate progressive glaucomatous damage. Early morning measurements are most frequently highest. The range of IOP may be as important, or more important than, the peak IOP level.