Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are rare, life-threatening mucocutaneous reactions characterized by extensive detachment of the skin. The incidences of SJS and TEN are rare (TEN: 0.4 to 1.2 cases per million). The eruptions can spread rapidly to the whole body within a day. Approximately 85% of patients have conjunctival lesions. Although high-dose corticosteroids, intravenous immunoglobulin (IVIG) and plasmapheresis have been attempted for treatment of SJS/TEN, the mortality rate is still high (TEN: 25 %). We recently showed that keratinocyte death in SJS/TEN can be triggered by the interaction of annexin A1 and formyl peptide receptor (FPR) 1 and may contribute to the pathogenesis of SJS/TEN. Annexin acts on FPR1, located on the surface of the skin cells, to cause necroptosis, a programed form of cell death. To develop FPR1 antagonist, we have generated the screening system including β-arrestin assay and calcium assay, and have started the screening.