Aeroallergens and food allergens are relevant eliciting factors of atopic eczema. This article focuses on the methods used for diagnosis in patients with suspected allergy to airborne or dietary allergens and who are suffering from atopic eczema. In addition to classical tests of IgE-mediated hypersensitivity (intracutaneous or in vitro testing), the role of provocation procedures is described. For aeroallergens, the atopy patch test yields the most specific results with regard to clinical history as compared with classical methods. For food allergens and pseudoallergic reactions to additives, this holds true for the double-blind, placebo-controlled food challenge. The methods and their limitations are discussed from a practical point of view.