Ninety-one subjects suffering from chronic or recurrent urticaria or recurrent angioedema of 2 months to 17 yr duration were skin-prick and scratch tested with 18 various food additives. Twenty-four of the subjects (26%) had at least one histamine equivalent skin test (ST) reaction. In contrast, only 24 (10%) of 247 non-urticaria control subjects showed comparable results. An oral provocation test with food additives was carried out on 10 of the 24 ST-positive subjects with urticaria or angioedema, but only one positive reaction, caused by benzoic acid, was recorded. All 91 subjects were advised to follow an additive-free diet. The effect of the diet was investigated with a retrospective postal survey. Twenty-three ST-positive subjects returned the questionnaire, 18 had followed the diet, and 16 (89%) of these 18 had experienced marked relief of their symptoms. Correspondingly, 42 of the 47 ST-negative subjects had followed the diet, and 17 (40%) had improved. The difference was significant (P less than 0.05). Our results suggest that skin tests with food additives can be used to measure skin hyperreactivity and that they may have a predictive value in identifying patients who will respond to an additive-free diet.