Acridine orange (AO) stains dsDNA green (525 nm) and RNA or single stranded DNA red (650 nm).The dye is membrane-permeant and its nucleic acid binding property has been used for cell-cycle studies. Acridine orange has also been used for the detection of microorganisms in cerebrospinal fluid and other clinical specimens. We offer a highly purified form of acridine orange while most of the other commercially available grades of AO are either in zinc chloride complex form or of low purity.