Certain food additives are known to induce urticaria and angioneurotic edema in susceptible patients. Thirty-three patients with chronic urticaria and angioneurotic edema whose case history suggested a possible link between exacerbations of the symptoms and ingestion of food additives or with acute exacerbations of the disease without any known triggering event were challenged orally in a double-blind study with increasing doses of the following additives: sodium benzoate, sodium metabisulfite and tartrazine and lactose as placebo. Ten of the 33 patients (30.3%) were intolerant to at least one compound. Among 132 oral provocation tests 11 (8.3%) were positive (appearance of acute urticaria/angioneurotic edema): 5 (15.1%) to sodium benzoate, 4 (12.1%) to tartrazine an 2 (6%) to sodium metabisulfite. There was no reaction to placebo and no serious reaction was observed. Under the conditions used, oral provocation tests proved to be feasible, safe and useful in the routine investigation of chronic urticaria and angioneurotic edema.