Eighty-nine and a half per cent of the population of a general practice over the age of 49 years were screened for glaucoma and high risk ocular hypertension requiring treatment. Screening took place using semi-automated intraocular pressure and visual field equipment operated by non-ophthalmologically trained staff. An experienced ophthalmologist examined all patients in a single blind manner to reduce false negatives to a minimum. Patients suspected of requiring treatment on the grounds of raised intraocular pressure, abnormal visual fields or suspicious optic discs were subsequently examined in a hospital clinic. Treatment criteria, as commonly practiced, were carefully defined and the sensitivities and specificities of the methods of screening used were calculated. One and three tenths per cent of the practice population were known to be receiving treatment prior to the study and a further 1.4% were found to require treatment after screening. The sensitivity and specificity of the non-contact tonometer were 91.7% and 95.6% respectively with a predictive power of 22.5% for a positive result. The mean time taken to perform the test in both eyes was two minutes. Seventy per cent of the patients with pressures over 22 mmHg in both eyes on screening were found to require treatment. The routine use of the field screener did not increase either the sensitivity or specificity of the screening process but its use in cases with raised intraocular pressure is advised to indicate the degree of urgency of the referral. An algorithm based on the results of the study is suggested when planning the use of semi-automated equipment to screen for ocular disease related to raised intraocular pressure.