Internucleosomal DNA fragmentation is a hallmark of apoptosis in mammalian cells. BioVision’s ApoDIRECT In Situ DNA Fragmentation Assay Kit provides complete components including positive and negative control cells for conveniently detecting DNA fragmentation by fluorescence microscopy or flow cytometry. The TUNEL-based detection kit utilizes terminal deoxynucleotidyl transferase (TdT) to catalyze incorporation of fluorescein-12-dUTP at the free 3’-hydroxyl ends of the fragmented DNA. The fluorescein-labeled DNA can then be observed by fluorescence microscopy or analyzed by flow cytometry.