The current practice and ideals of ophthalmologists when alerting and screening siblings at risk of chronic simple glaucoma were assessed by means of a questionnaire. Seventy-nine per cent of Trent Region consultants responded, and of these, 18% do not attempt to alert siblings of glaucoma sufferers. Those who do rely on the probands to alert their siblings and the high street optometrists to screen. Under more favourable conditions, all respondents would advise screening for siblings over 40 years of age. Fifty-nine per cent would then advocate the letter as the optimum method of communication and 78% would prefer that an ophthalmologist screen this high risk group. In a pilot study of a hospital-based screening service, siblings living within a 15 mile radius of the hospital were invited by letter to attend for screening. Ninety per cent attended, of whom 12.5% required treatment and a further 11% careful observation. The cost of detecting a case of treatable disease by this strategy was estimated at 138 pounds.