The intra-ocular pressure of 1078 general practice patients aged over 45 years was measured with the Schiötz tonometer. Primary open-angle glaucoma was found in 29 patients (2.7%) and ocular hypertension in 40 (3.7%). The technique of using the tonometer is described and a plea is made for general practitioners to make more use of it in screening their patients for glaucoma.