Ranitidine is an H2-receptor antagonist which is usually well tolerated. Hypersensitivity reactions to ranitidine, as well as other H2 antihistamines, have been rarely described. We report the case of a 47-year-old woman who developed an anaphylactic reaction to ranitidine used as intravenous premedication before anesthesia induction. The patient's history revealed that previous use of oral ranitidine for a peptic ulcer disease did not cause any adverse reaction. Intradermal test with ranitidine at a dilution of 1:100 gave an intense positive reaction. The protective role of H2-receptor antagonists as premedication is still unclear and should be carefully reconsidered on the basis of the available controversial evidence and the possible risk of hypersensitivity reactions.