The aim of the study was to investigate the safety to allergic patients of 19 commercially available and authority-approved enzymes used in the food industry. Enzymes produced by genetically modified organisms were included. Four hundred consecutive adult patients with a diagnosed allergy to inhalation allergens, food allergens, bee or wasp were included. All had at least one positive skin prick test to the above allergens.Skin prick testing with the 19 enzymes was performed on the forearm and if positive (in 13 patients), in vitro histamine release from blood basophils were performed. Patients with positive results in skin prick test were subsequently reinvestigated with further purified enzymes and finally challenged orally with the enzymes in a double-blind, placebo-controlled protocol. Only one reaction to a placebo challenge was seen.In some instances a positive skin prick test result or a positive histamine release was seen elicited by the enzymes, but since none of the patients were positive to any of the commercial enzymes in the subsequent oral challenges using exaggerated dosages of the enzymes compared to normal daily intake, the findings are without clinical relevance.A wide variety of enzyme classes and origins was included in the study. Because there were no allergenic findings of clinical relevance it is concluded that ingestion of food enzymes in general is not considered to be a concern with regard to food allergy.