Investigation of urticaria in a young woman disclosed a hypersensitivity to menthol. Innocent systemic or percutaneous exposure to this very common substance had also elicited "hot flashes" over several years, but recognition of the symptom as an urticarial equivalent required hindsight. Production of these clinical manifestations and of a histamine headache followed different provocative tests. This was associated with a diagnostic drop in the number of circulating basophil leukocytes.