Possible sequelae of improper administration of eyedrops include treatment failure, unnecessary use of additional medications and spread of infection. To determine the extent of improper topical self-application of ocular medications, 150 patients with glaucoma who were already using eyedrops were studied. Employing their customary methods of administration 19 (13%) of the patients were unable to place drops in both eyes after one or more attempts, and 120 (80%) of the patients failed to maintain the bottle's sterility during application. No significant relation was found between performance and age, sex, educational level, visual acuity or field, intraocular pressure, length of time the patient had been using eyedrops or, among the 100 clinic patients, whether the patient had received prior instruction in their use. The 50 private practice patients had all received prior instruction, by one physician, whereas only 62% of the clinic patients had, and there had been several instructors at the clinic. Significantly more (p less than 0.05) of the clinic patients than of the private practice patients failed to wash their hands before instilling the drops (97% v. 78%) and were unable to properly instil the drops in both eyes after one or more attempts (18% v. 2%). Therefore, uniform teaching probably improves the ability of patients to topically administer ocular medication.