SummaryQuantification of human basophil degranulation induced by anti‐IgE, anti‐IgG4, and by ionophore was performed using a flow‐cytometric system. It was shown that these antibodies and ionophore can degranulate basophils in a dose‐dependent manner, and that there is a wide variation in the response of basophils obtained from different individuals to these stimuli. A significant correlation was observed between the degree of degranulation induced by anti‐IgE and anti‐IgG4, while this was not the case for anti‐IgE and ionophore. It was also shown that IgG4 myeloma protein can passively sensitize basophils. In general, degranulating efficacy was in the order of ionophore>anti‐IgE>anti‐IgG4, both in allergic and non‐a