Clinical report and investigation of a patient with localized heat urticaria.

Localized heat urticaria is a rare disorder, in which the nature of the mediator is not fully established. We report the case of a 41-year-old woman with the condition, dependent upon mast cell integrity, in which histamine was demonstrated as the dominant, if not sole mediator. Non-sedative antihistamines conferred some therapeutic benefit, but subsequent sequential desensitization has enabled her to lead a full and active life again.