Local anaesthetics are known to cause commonly adverse reactions, most of them are due to adjoining substances (vasoconstrictors and preservatives). Allergic reactions are rare. Lidocaine is one of the most frequently local anaesthetics used in current medicine. Case report: a 54 year old woman, with an adverse reaction to metamizol, who came to our allergy service for study the reaction with the drug implicated and also to made a pre-anaesthetic assessment before going into a surgery. According our protocol we performed skin prick-test with mepivacain, thiopental, propofol, pancuronium bromide, suxamethonium, lidocaine, diacepam and latex. Patch test with mepivacain, bupivacaine and lidocaine were also carried out. We made drug intramuscularly challenges, with mepivacain 2%, bupivacaine 0,5% and lidocaine 2% and an oral challenge with metamizol. All the skin prick test was negative. Six hours after the administration of lidocaine the patient present a pruritic and erythematous cutaneous wheal (10×10 cm) in the local injection area. The rest of the challenges were negative. The patch test with lidocaine was positive at 48 hours and also at 96 hours, with bupivacaine and mepivacain were negative. Eight controls were negative. We present a patient with delayed hypersensitivity to lidocaine, demonstrated by patch test and a positive delayed result in the intramuscularly challenge.