The single cell gel electrophoresis (SCGE),also called comet assay,is a simple,sensitive,rapid and inexpensive detection technique of DNA breakage in individual mammalian cell.It has been used in both in vivo and in vitro studies to assess DNA damage and repair induced by various agents,such as physical factors,e.g. UV,radiation,chemical factors,e.g. oxidants, trichloro-ethylene, acrylamide,bleomycin,as well as ageing and smoking,in a variety of mammalian cell lines. A panorama of the development of the SCGE assay，the mechanism and the procedures of the method，and its potential applications in DNA damage and repair，biomonitoring，cancer therapy researches，etc. is given.