In patients with a history of anaphylactic sting reactions, in-vitro tests are performed in order to demonstrate venom sensitization to the causative venom. Measurement of specific IgE-antibodies (sIgE) to the natural composite venom represents the standard in-vitro method to demonstrate venom sensitization. If sensitization to the composite venom cannot be demonstrated, one may determine sIgE to recombinant allergen compounds, in order to demonstrate sensitization to molecular venom allergens. Moreover, several cellular tests are available to confirm venom sensitization. Herein basophils, which carry cell-bound sIgE, can be used to produce a confirmatory response upon incubation with venom allergens. Reactions to both honey bee and vespid venom may either indicate true double sensitization or cross sensitization. The identification of antibodies cross-reacting to venoms and to other allergen sources does not exclude clinical relevance. Elevated baseline serum tryptase is a risk factor for severe systemic reactions after a field sting and during venom immunotherapy (VIT), the latter in particular for VIT with vespid venom. Serum tryptase measurement should, therefore, be included into routine diagnostics of venom allergy. The measurement of IgG-antibodies specific to venom is not recommended for routine work-up. None of the mentioned in-vitro tests, which may be used before, during or after VIT, allow, however, a precise prognosis with respect to future sting reactions, or to side effects and to the efficacy of VIT, respectively. To validate the reason for a VIT, one should also consider patient history and results of other tests.