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Objective: Imidazoline derivatives like naphazoline have a firm place in diagnostics and therapy of otorhinolaryngology because of their vasoconstrictive and decongestive properties. Their alpha-adrenergic potential could induce not only local but also systemic side effects like hypertension and tachycardia which can increase a life-threatening intoxication. Signs of imidazoline intoxication are excessive systolic and diastolic hypertension and hypotension, bradycardia with arrthyhmia, respiratory depression, excitation or severe CNS depression. Patients: The typical course of an intoxication and its sufficient therapy is reported by means of two cases of intraoperative application of naphazoline for hemostasis. Results: In case of overdosage or intoxication, symptomatic drug therapy with intravenous administration of 5 mg phentolamine for adults and 1 mg phentolamine for infants has to be done. Phentolamine, an alpha-adrenoceptor antagonist, acting against peripheral and central side effects has to be used because no specific antidote is available. Conclusions: Especially pediatric otorhinolaryngologists have to know about symptoms and therapy of an intoxication after application of naphazoline. Particularly with children, a narrow therapeutic to toxic window can be observed in this frequently used drug.