The Cellular Antigen Stimulation Test (CAST) is a new method of in-vitro-diagnosis of allergic reactions. The test based on the prestimulation of blood leukocytes with cytokine IL-3 and the exposure to allergens. Mainly basophiles react by synthesizing sulfido-leukotrienes LTC4 and its metabolites LTD4 and LTE4, which can be detected by ELISA technique. 84 patients with suspected allergy to hymenoptera venoms were investigated by means of the CAST, CAP and the skin tests. Allergic reactions comprised all severity grades (I - IV ref. H.L. Mueller). The allergolocial work-up included skin test (up to 1 mu g/ml), the measurement of specific IgE-antibodies by CAP system and Cellular Antigen Stimulation Test. The CAST was carried out with a concentration of 0,2 mu g/ml bee and wasp venom (Apis mellifera, Vespula spec.), respectively. A control group of 10 non-allergic CAP-negative individuals was established. Diagnostic accuracy of CAST was evaluated by comparison with the skin tests and CAP. With bee venom a sensitivity and specificity of 93/67% was obtained, while wasp venom showed 96/63% sensitivity and specificity. In our investigations the CAST showed better results in comparison to CAP results. In some cases pseudoallergic reactions could be detected after incubation with C 5a.