Biological standardization of allergen extracts is one of the steps in the characterization of an extract. The gold standard for determination of biological potency is the skin prick test, but histamine release (HR) has been used as a convenient ex vivo method for analyzing a large number of samples. We describe the use of rabbit basophils as a tool in biological standardization. Using peanut as a model allergen, it is described how rabbits immunized for production of antiserum may become sensitized and their basophils used for histamine release experiments. It is also possible to use rabbit antiserum to passively sensitize basophils derived from naive rabbits, but the sensitivity of this method is so far 100-1000 times lower than the direct histamine release. The rabbit histamine release results are compared to an ELISA developed by means of the same antisera and by passive sensitization of human basophils using serum from a strongly sensitized peanut-allergic patient. The overall sensitivity of the methods were ELISA > HR-human cells > HR-sensitized rabbit cells > HR-passively sensitized rabbit cells. The use of rabbit basophils for biological standardizations will allow for the use of rabbit antisera.