Adverse reactions to foods may arise by a variety of mechanisms, both immune (IgE and non-IgE) and non-immune mediated. This article considers those assays useful in the diagnosis of Type 1 hypersensitivity to foods (IgE-based) and, importantly, discusses those assays where evidence is lacking for their use. In all cases of suspected food allergy, a full clinical history is indispensable in facilitating diagnosis. Total serum IgE is not a suitable screen for food allergy. Suspect allergens may be confirmed by either skin prick testing or serological assays for specific IgE. Several studies suggest concentrations of food-specific IgE at which there is a high probability of reaction on food challenge. These cut-off levels are now being used by physicians to direct clinical advice. However, it is important to note that not all studies agree on these limits and the chosen cut-off is dependent on the population studied and the assay used.