The aim of the article is to introduce the atopy patch test (APT) as a model of cellular immunity reaction. APT is epicutaneous test performed with food and aeroallergens, and represents a good model for T lymphocyte hypersensitivity. It is compared with skin prick test (SPT). Its value is supported by the fact that atopic dermatitis is the result of complex immune interactions and involves both Coombs and Gell reactions type IV and I. In this review, we shortly discuss the etiopathogenesis of atopic dermatitis, distinction of extrinsic and intrinsic issues, and compare the value of APT with SPT and IgE determination. APT includes epicutaneous application of type I allergens known to elicit IgE mediated reactions, followed by evaluation of eczematous skin reaction after 48 and 72 hours. The limitations of ATP include the lack of test standardization, but there also are comparative advantages over SPT and specific IgE determination. We also briefly discuss the most important food and aeroallergens. APT has been recognized as a diagnostic tool in the evaluation of food allergy and aeroallergens such as house dust mite, pollen and animal dander. APT is a useful diagnostic procedure in patients with atopic dermatitis allergic to inhalant allergens and in children with food allergy younger than 2 years. The sensitivity and specificity of the test greatly depend on the allergen tested and patient age.