Numerous undesirable reactions to alcoholic beverages, foods, drugs and other substances are characterized by allergy-like signs and symptoms and yet show unambiguously negative allergy test results. Such persons should be assessed for evidence of histamine intolerance caused by histamine overload and/or diamine oxidase deficiency. Diamine oxidase is the main histamine degrading enzyme with a predominantly gut activity. This would explain why nutritional allergies are often primarily suspected. The clinical evidence for histamine intolerance is based on chronic headache, diarrhoea, vomiting, flush, urticaria, asthma-like symptoms, rhinitis and others. Histamine restricted food, supported if necessary by H1 antihistamine blockade are simple but highly efficacious measures as shown by us in large patient groups. Intolerance to red wine probably is the most outstanding clinical characteristic and a directed question must be included into any allergy history in order to avoid missing a very major diagnostic spectrum with good therapeutic maneuverability.