PURPOSE: To observe eye drop instillation technique in chronic glaucoma patients. METHODS: This is a prospective study enrolling 193 glaucomatous patients. Each received a sample of lubricant eye drop bottle (Dunason®, Alcon Laboratories, Sao Paulo, Brazil) and was instructed to use it once. RESULTS: All patients used a mean amount of 1.64 ± 1.26 drops. In 54.5% of the patients, the eyedropper touched the eye and adnexa. In 3.1% the drops were not placed in the eye, without the patient being aware of this. In 87.0% of them, neither the lacrimal point occlusion nor the closure of the eyes for two minutes after instillation were observed, and 61.6% repeatedly blinked right after instilling the drop. CONCLUSIONS: Most patients did not use the eye drops properly. That may result in some undesirable consequences, such as, a partial wastage of the bottle's content, a possible increase in systemic toxicity, the risk of contamination of the bottletip, and, mainly, a decrease in the full hypotensive effect of the drugs. Therefore, the patients have to be carefully taught the correct way to use eye drops.