It is not known whether trace amounts of proteins that may remain in cereal-starch-derived food ingredients even after food processing can trigger allergic symptoms in cereal-allergic individuals. The aim of this study was to find out if barley starch syrup causes allergic reactions in patients with allergy to wheat, barley, rye or oats. Fifteen children with allergy to these cereals, confirmed by double-blind placebo-controlled food challenge (DBPCFC), were selected for the study. When exposed to cereals, seven of the children (47 %) showed immediate type reactions, such as urticaria, rash or anaphylaxis. Eight of the children (53 %) showed delayed type reactions, such as deterioration of atopic dermatitis or diarrhoea. The fifteen children with allergy to cereals were exposed to barley starch syrup in DBPCFC and none of them showed any objective signs of allergy. On skin-prick tests (SPT), five of the children (33·3 %) showed a positive ( ≥ 3 mm) reaction to at least one of the cereals but none of them to barley starch syrup. This study confirmed with 98 % confidence that at least 90 % of the patients with verified allergy to cereals will not react with allergic symptoms to barley starch syrup.