Abstract We have investigated the electrochemical detection system of allergic reaction using rat basophilic leukemia (RBL-1) cells by applying cyclic voltammetry. When the potential of the electrode is run in the range 0—1.0 V versus a saturated calomel electrode (SCE), an anodic peak current appears around 0.34 V. This peak current or RBL-1 cells is attributed to intracellular serotonin. After the addition of allergen, this peak current increases with time and the maximum current (0.82 μA per 2×10 5 cells) is obtained after 20 min. On the other hand, the current is constant when the allergen is not added. This current increase is attributed to localization of the intracellular serotonin and is specific for allergen.