In a clinical study 90 patients with chronic or chronic relapsing urticaria underwent a standardized diagnostic programme. In 61% of the cases no causing factors were to be found. In the remaining 39% the most common causes were represented by intolerance reactions (16%), infection causes (16%) and physical causes (13%). To some extent multiple causes were present. In the case of substances intolerance causing, it was a matter of medicine (acetylsalicylic acid and other analgetics) in three quarters (12%) and of food additives (benzoate, sorbic acid, tartrate yellow and sunset yellow) in one quarter (4%). There was not a case in which food itself was a cause, neither in the sense of intolerance reaction nor in the sense of a true allergy. In 13% of the patients, who became symptom-free during the elimination diet, no causes whatsoever could be found neither in oral provocation tests nor in provocation diets. At present we are still in the dark if impurities in foodstuffs (antibiotics, yeasts, moulds etc.) could play a role in these cases.