The basophil activation is emerging as a reliable and robust in vitro biomarker of in vivo allergy reactions. Basophil Activation Test (BAT), intended as in vitro stimulation of patient blood basophil with allergens, followed by flow cytometric detection and quantification of such activation, is nowadays a well-established assay in a growing number of routine diagnostic labs. The advancements in the standardization of BAT testing and first convincing clinical evidence are behind this spreading of the assay in clinical lab. BAT is essentially an assay with superior specificity compared to any other allergy testing and, if appropriately used, it can have a valuable clinical utility in different field of allergy diagnosis. In drug allergy, very few testing opportunity are available for the numbers of drugs actually in the market. Antibiotics and analgesics are just two of the categories of drugs were BAT testing can have an added value for the limited specificity of IgE testing or limited availability of other lab testing. In food allergy, BAT is emerging as the more accurate assay to predict an in vivo reaction to food, helping in the discrimination of patients that are only sensitized versus the patient really allergic to an allergen. Furthermore BAT testing determining the basophil sensitivity can be useful for monitoring the natural resolution of allergies and clinical responses to immunomodulatory treatment for food allergies. For this characteristic, BAT has the potential to reduce the need of Oral Food Challenge (OFC). In the hymenoptera venom allergy, BAT is an effective tool in identifying primary sensitizing antigen and in the follow up of patient in venom immunotherapy. With this review, we want to present current state of BAT testing focusing on the clinical laboratory parameters and issue of this assay. A highlight on the standardization needs of BAT is provided, together with considerations on further developments and clinical evidences still to be achieved.