Homidium Free Base is a trypanocidal agent and possible antiviral agent that is widely used in experimental cell biology and biochemistry. Ethidium has several experimentally useful properties including binding to nucleic acids, noncompetitive inhibition of nicotinic acetylcholine receptors, and fluorescence among others. It is most commonly used as the bromide.

Homidium Chloride is the chloride salt of ethidium (a fluorochrome), Ethidium Chloride intercalates within double-stranded nucleic acids, particularly DNA. In molecular biology, the bromide salt of ethidium is used to detect and visualize DNA after electrophoresis or in cytochemical preparations. In veterinary pharmacology, it is used as a trypanosomicide. Ethidium bromide and chloride are toxic substances and potent noncompetitive antagonists of the nicotinic acetylcholine receptor.