Ethidium bromide (EtBr) is mainly used as a non-radioactive marker for detecting double-stranded DNA in gels. EtBr is a DNA intercalator. It shines brighter after inserting itself between the base pairs in the double helix and fluoresces readily when exposed to UV light, making it easy to detect.

EtBr can also be used to stain single-stranded DNA or RNA, however it is less sensitive for these molecules, often requiring about ten times more nucleic acid for equivalent detection.