Anaphylaxis is a systemic, immediate, hypersensitivity reaction that usually occurs because of foods, insect stings, or drugs (1, 2). Exercise-induced anaphylaxis (3) and, recently, food-dependent, exercise-induced anaphylaxis also have been reported (4, 5). Idiopathic anaphylaxis refers to anaphylaxis of unknown cause (6-8). We have studied a group of 50 patients with idiopathic anaphylaxis, including a group of 31 patients previously described by Sale and associates (6). An updated description of the evaluation, treatment, and clinical course of these patients is presented here. Fifty patients with idiopathic anaphylaxis had one or more life-threatening reactions manifested by urticaria or angioedema accompanied by