Allergies are frequent and approximately 30% of the general population in Germany are affected. The specific sensitization against an allergen is asymptomatic. On renewed allergen contact the symptoms are indicative of the underlying pathomechanism. A variety of different test procedures are available to identify allergic reactions.In this review article the typical clinical symptoms of allergic reactions are assigned to mechanisms and possible test methods are presented and discussed. Current developments in recombinant serum diagnostics and cellular testing methods are presented.