The effect of body position on the intraocular and blood pressures of normal volunteers and of patients with ocular hypertension and low tension glaucoma was studied. Changing from the sitting to the supine position increased the intraocular pressure by an average of 4.4 (SD 2.0) mm Hg in the control group, 4.0 (SD 2.0) mm Hg in the ocular hypertension group, and 4.1 (SD 1.8 mm Hg) in the low-tension glaucoma group. After 30 minutes in the supine position the intraocular pressure in normal volunteers and patients with low tension glaucoma remained stable. In contrast patients with ocular hypertension showed a further significant increase in intraocular pressure of 1.6 (SD 2.8) mm Hg (p = 0.004). This was accompanied by an equally significant decrease in blood pressure (p less than 0.001). We believe that these are manifestations of different mechanism of intraocular pressure regulation between these groups.