The diagnosis of asthma is based primarily on patient history, conducting the interrogation to the search for risk factors for developing it and the triggers of their symptoms. This chapter will detail some laboratory tests and cabinet that can support this clinical diagnosis. Respiratory function tests help to show the degree of airway obstruction and its reversibility with treatment. Allergy tests help prove the existence of cells sensitized to a specific allergen and once identified, implement environmental control measures or if necessary to control this immunomodulation exaggerated immune response. The exhaled nitric oxide test has been most useful in assessing the course of asthma during treatment, rather than for diagnosis. Sometimes the confirmatory diagnosis of asthma is achieved after excluding other diseases that may present a similar clinical picture, and especially after knowing the response to standard treatment with bronchodilators and anti-inflammatory drugs.