Chronic urticaria exacerbated by the antioxidant food preservatives, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Two patients with chronic idiopathic urticaria in whom remissions were achieved with dye- and preservative-elimination diet had exacerbations of their urticaria when they were challenged under double-blind, placebo-controlled conditions with butylated hydroxyanisole and butylated hydroxytoluene. After elimination of butylated hydroxyanisole and butylated hydroxytoluene from their diets, there was marked abatement of the frequency, severity, and duration of their urticaria. These antioxidants appear capable of aggravating symptoms in certain patients with chronic urticaria. 