Blood pressure was monitored for 24 h in 32 control patients, 38 open-angle glaucoma patients referred because of decompensated IOP despite maximum treatment, 40 patients with open-angle glaucoma referred because of progressive damage despite controlled IOP, and 39 normal-tension glaucoma patients. In the control group a physiological drop in blood pressure during the night was observed. The patients referred with uncontrolled IOP had blood pressure very similar to that of the control group during both day and night. However, the open-angle glaucoma patients with progression despite well-controlled IOP and also the patients with normal-tension glaucoma had markedly, and statistically significantly, lower systolic blood pressure during both day and night. The difference in diastolic blood pressure was smaller. Thus, blood pressure should be considered in diagnosis.