The application and development of new in vitro techniques aims to enable a diagnosis to be reached while incurring no risk for the patient, a situation which is particularly desirable in the case of severe reactions like anaphylaxis. The in vitro diagnosis of anaphylaxis includes, among other aspects, the serial measurement of mediators which are released in the course of an anaphylactic reaction such as tryptase, histamine, chymase, carboxypeptidase A3, platelet-activating factor and other products from mastocytes. The detection of agents which trigger the anaphylactic reaction can be made with the use of serologic methods: serum-specific IgE or with cellular tests which measure the release of basophil mediators (leukotrienes, histamine) or with the analysis of the expression of basophil markers, a technique known as the basophil activation test. These techniques offer interesting alternatives in the diagnosis of anaphylaxis. The basophil activation test provides important advantages in patients with anaphylaxis to beta-lactams, non-steroidal anti-inflammatory drugs, neuromuscular blocking agents and drugs where there is no technique to measure specific IgE.