BACKGROUND. Previous studies have shown that for every known case of glaucoma there is another case of occult disease. Most cases of glaucoma are detected by optometrists. AIM. This study set out to determine the prevalence of occult glaucoma in a practice population and assess the likely resource implications of introducing a glaucoma screening programme into a general practice setting. METHOD. The 1153 patients registered with one practice in Leicester who were aged 55-69 years on 1 January 1992 and who were not known to have glaucoma prior to screening were invited to a screening clinic. Prior to screening there were 11 known cases of glaucoma in this age group. Screening was carried out by a practice nurse. Patients who failed the screening tests were referred according to the study protocol to the ophthalmology department of the Leicester Royal Infirmary and examined by one ophthalmologist. The number of cases of occult glaucoma and other eye disease detected, the cost per case screened and case detected, and the number of referrals generated were evaluated. RESULTS. Nine hundred and fifty people (82%) accepted the invitation and attended for glaucoma screening. Of those screened 115 (12%) were referred for ophthalmic assessment. Glaucoma was confirmed in 14 of the referred patients (12%) while a further 15 (13%) were found to have ocular hypertension. All but one of those people diagnosed as having glaucoma recalled having been examined by their optician within the last five years; for 50% the period was less than two years. Nineteen of the patients referred (17%) had other ocular pathology detected by the ophthalmologist and no abnormality was detected in 65 patients referred (57%). The estimated cost to the practice (excluding hospital outpatient costs) per case screened using the study protocol was 6 pounds and the cost per case detected was 408 pounds. CONCLUSION. Glaucoma screening may be successfully undertaken in a general practice setting by non-ophthalmically trained staff who have received tuition in the use of the equipment. It is well received by the population served but the capital cost of equipment is likely to be too high for most practices to afford. The reaffirmation of at least one occult case of glaucoma for every known case is particularly alarming in the absence of a national screening programme and the asymptomatic course of this treatable, blinding disease. Closer cooperation between general practitioners and optometrists will be the practical way ahead for most practices.