Cell Meter™ TUNEL apoptosis assay kit provides a robust tool for conveniently detecting apoptosis caused by DNA fragmentation. The assay is non-radioactive and rapid. The TUNEL assay uses the terminal deoxynucleotidyl transferase (TdT) to catalyze the incorporation of TMR-dUTP at the free 3€™-hydroxyl ends of the fragmented DNAs. The resulted TMR-labeled DNAs are analyzed by fluorescence microscopy (Cy3 or TRITC filter set). Its red emission can be conveniently multiplexed with GFP labelled targets. Direct incorporation of fluorescent TMR-labeled nucleotides significantly reduces the number of test steps. The kit is optimized to detect apoptosis in fixed cells and formalin-fixed, paraffin-embedded tissue sections.