DAPI is a cell-permeable DNA-binding dye which binds preferentially to DNA rich in adenine and thymine. It is used in flow cytometry for measuring nuclear DNA content or for sorting isolated chromosomes and is also useful for microscopic detection of nuclei and nuclear DNA in normal and apoptotic cells. DAPI can also be used to detect mycoplasma and in simple retrograde double-labelling procedures for studying axonal branching employing Evans Blue and Primulin. DAPI is a reversible inhibitor of S-adenosyl-L-methionine decarboxylase and KAO (diamine oxidase).