Is DAPI toxic to cells?

DAPI is toxic to cells, and once live cells are stained, they will not survive for an extended period of time. Thus, DAPI is preferred for staining fixed cells as opposed to live cells. DAPI is also a known mutagen and should be handled with the proper precautions. On a side note, Hoechst 33342 dye has been shown to be more toxic to CHO cells than DAPI.