Peanut is one of the major food allergens inducing anaphylaxis. It is increasingly consumed and often used as a hidden ingredient, thus making avoidance especially difficult for allergic patients. In Switzerland legislation stipulates that all ingredients of a processed food exceeding 2% of the total mass of the finished food product should be labelled. However, in the case of a mixture of vegetables it can be labelled as "vegetable mix" if it does not exceed 10% of the total weight. Peanut, which is a member of the legume family, can thus form up to 10% of processed foods without being mentioned on the label, thus making avoidance impossible. We report on two patients who presented severe anaphylaxis from peanut hidden in a pizza from a fast food restaurant. We were able to provide evidence for the presence of major peanut antigens in the pizza sauce by immunochemical analysis. These two cases clearly demonstrate the danger of peanut hidden in foods and point up the necessity of a change in legislation.