Immediate allergy is caused by a chemical mediator released from basophile and mast cells via cell degranulation due to reaction betweeen an immunoglobulin E (IgE) antibody, bound with the IgE receptor on the cell membrane, and an antigen. The present authors have established a new method for assaying the enzyme activity of β-hexosaminidase as an index of chemical mediator release. Using cultured cells instead of conventional methods based on histamine release from mast cells, the present method permits highly accurate mass screening since it uses a well-established cell line of rat basophilic leukemia cells(RBL-2H3). The effects of metal elements on immediate allergic reaction were evaluated using a newly developed assay system.A total of 38 metal elements were investigated for effects on immediate allergic reactions in vitro. These elements were classified by five types on the basis of action on β-hexosanimidase release : 1) those which showed very strong inhibitory action, such as ZnCl₂ and ZrCl₄, 2) those which showed relatively strong inhibitory action, such as CdCl₂ and CuCl₂, 3) those which showed relatively weak inhibitory action, such as CoCl₂ and Pb(NO₃)₂, 4) those which showed neither inhibitory nor promoting action, such as MnCl₂ and SrCl₂, and 5) AgNO₃, which alone showed promoting action.