Single cell gel electrophoresis; a method for assessing DNA damage in individual cells caused, for example, by apoptosis, radiation or chemical mutation. Cells embedded in an agarose gel are subjected to electrophoresis and stained with a DNA-binding dye. If the DNA is fragmented by double-strand breaks, small fragments will migrate toward the anode and under the microscope will appear as a central fluorescent body, the nucleus, and a smaller body, the fragments, giving the appearance of a comet head and tail. Alkaline treatment of the cells before electrophoresis will increase the sensitivity of the assay by denaturing the DNA, thus allowing detection of single-strand breaks.