BACKGROUND: Chlorhexidine is a synthetic biguanide with a broad antibacterial activity and has become an important cause of perioperative anaphylaxis.OBJECTIVE: Reactions due to chlorhexidine allergy are usually IgE-mediated. The aim of this report is to demonstrate utility of laboratory in-vitro testing for diagnosis.METHODS: We report the case of a 36-year old man who experienced severe anaphylaxis during general anesthesia. He underwent skin tests, specific detection of specific IgE to chlorhexidine and basophil activation test (BAT).RESULTS: Skin tests gave false positive results due to dermographism. So, on the basis of a clinical reaction to chlorhexidine and positive tests for IgE to chlorexidine and BAT, we assessed the diagnosis of chlorhexidine allergy.CONCLUSIONS: Physicians should be aware of the role of chlorhexidine in the etiology of perioperative anaphylaxis. In vitro testing such specific IgE and BAT are useful in patient with suspected chlorexidine allergy and limitation to perform skin tests.