Immunologic and immunochemical methods are valuable tools in the investigation of food allergens and antinutritial proteins. Protease inhibitors and lectins are present in a broad spectrum of foods. They can retain their activity during passage through the digestive tract and induce different biological reactions, beneficial as well as harmful. The potential nutritional importance of legume inhibitors and lectins is evaluated from analyses of their concentration, biological activity and their stability during food processing conditions. Food allergens comprise a very varied group of proteins and glycoproteins with different sensitization routes for children and adults that are currently discussed. Food allergens' induction of oral tolerance was investigated by oral immunization of mice with milk or β-lactoglobulin.